Association between fetal fraction on cell-free DNA testing and first-trimester markers for pre-eclampsia

The Association between Low Fetal Fraction of Non-Invasive Prenatal Testing and Adverse Pregnancy Outcomes for Placental Compromise

(1) Background: Non-invasive prenatal testing (NIPT) is a screening test for fetal aneuploidy using cell-free fetal DNA. The fetal fragments (FF) of cell-free DNA (cfDNA) are derived from apoptotic trophoblast of the placenta. The level of fetal cfDNA is known to be influenced by gestational age, multiple pregnancies, maternal weight, and height. (2) Methods: This study is a single-center retrospective observational study which examines the relationship between the fetal fraction (FF) of cell-free DNA in non-invasive prenatal testing (NIPT) and adverse pregnancy outcomes in singleton pregnancies. A total of 1393 samples were collected between 10 weeks and 6 days, and 25 weeks and 3 days of gestation. (3) Results: Hypertensive disease of pregnancy (HDP) occurred more frequently in the low FF group than the normal FF group (5.17% vs. 1.91%, p = 0.001). Although the rates of small for gestational age (SGA) and placental abruption did not significantly differ between groups, the composite outcome was significantly higher in the low FF group (7.76% vs. 3.64%, p = 0.002). Furthermore, women who later experienced complications such as HDP or gestational diabetes mellitus (GDM) had significantly lower plasma FF levels compared to those without complications (p < 0.001). After adjustments, the low FF group exhibited a significantly higher likelihood of placental compromise (adjusted odds ratio: 1.946). (4) Conclusions: Low FF in NIPT during the first and early second trimesters is associated with adverse pregnancy outcomes, particularly HDP, suggesting its potential as a predictive marker for such outcomes.

Cell‑free fetal DNA at 11‑13 weeks of gestation is not altered in complicated pregnancies

Non-invasive maternal cell-free fetal DNA (cffDNA) is a promising biomarker for screening common genetic syndromes. Alterations in the expression levels of cffDNA in the maternal circulation have been demonstrated in abnormal pregnancies. However, the results are conflicting. The present study aimed to investigate whether cffDNA levels are associated with pregnancy complications. The study group comprised pregnant women who presented with pregnancy complications, such as preterm birth, gestational hypertension, intrauterine growth retardation, gestational diabetes, polyhydramnios, oligohydramnios, vaginal bleeding and placental abruption. The control group comprised women who had a normal pregnancy course. Blood samples were obtained from 500 pregnant women between 11-13 weeks of gestation. cffDNA was amplified, sequenced and analyzed using the next-generation aneuploidy test of a Panorama-Natera kit. Nuchal translucency (NT) thickness as well as pregnancy associated plasma protein-A (PAPP-A) and β-human chorionic gonadotropin (β-hCG) levels were also assessed. Statistical analysis was performed in 494 out of the 500 samples collected with SPSS v.26 using non-parametric methods. The parameters were normalized by the multiples of median (MoM) method. The expression levels of PAPP-A, β-hCG, and the NT mean MoM values were significantly different between the study and control groups (P=0.005, P<0.001 and P=0.007, respectively). However, the expression levels of cffDNA and the mean MoM values were not significantly different between these two groups (P=0.687). The findings of the present study support the conclusion that cffDNA expression is not altered in a series of pregnancy complications. The prognostic value of cffDNA in predicting adverse pregnancy outcomes requires further investigation.

Insights into non-informative results from non-invasive prenatal screening through gestational age, maternal BMI, and age analyses

The discovery of cell-free fetal DNA fragments in the maternal plasma initiated a novel testing method in prenatal care, called non-invasive prenatal screening (NIPS). One of the limitations of NIPS is the necessity for a sufficient proportion of fetal fragments in the analyzed circulating DNA mixture (fetal fraction), otherwise, the sample is uninterpretable. We present the effect of gestational age, maternal body mass index (BMI), and maternal age on the fetal fraction (FF) of the sample. We retrospectively analyzed data from 5543 pregnant women with a single male fetus who underwent NIPS from which 189 samples received a repeat testing due to an insufficient FF. We showed the relationship between the failure rate of the samples after the repeated analysis, the FF, and the gestational age at the first sampling. Next, we found that different maternal BMI categories affect the FF and thus the chance of an informative redraw. A better understanding of the factors affecting the FF will reduce the number of non-informative calls from repeated analyzes. In this study, we provide helpful information to clinicians on how to approach non-informative analyses.

Cell free DNA screening for fetal aneuploidy in Ireland: An observational study of outcomes following insufficient fetal fraction

OBJECTIVES

To determine maternal factors associated with low fetal fraction (FF). To determine the proportion of women who receive a result from repeat non-invasive prenatal testing (NIPT) testing. To identify any significant associations between pregnancy interventions or outcomes and low FF.

STUDY DESIGN

Retrospective observational study of 4465 women undergoing antenatal screening by targeted cell free DNA (cfDNA) testing at an Irish tertiary maternity hospital between January 2017 and December 2022. Patients who failed to obtain a result after the first NIPT were analyzed in two cohorts; those who received a result on a repeat sample and those who failed to ever achieve a result despite a second, third or fourth cfDNA test.

RESULTS

Risk of insufficient FF significantly increased with elevated maternal BMI (OR 1.07; 95% CI 1.01-1.13, p = 0.03) and in-vitro fertilization (IVF) (OR 3.4; 95% CI 1.19-9.4, p = 0.02). Women with no result were more likely to have diagnostic invasive testing (p < 0.01), but had no increased risk of aneuploidy. Repeated failed NIPT attempts due to low FF were significantly associated with the subsequent development of hypertensive diseases of pregnancy (p = 0.03). Greater than 70% of patients who were unsuccessful in a first or second attempt at NIPT due to low FF yielded a result following a second or third sample.

CONCLUSIONS

High BMI and IVF conceptions are greater contributors to low FF than fetal aneuploidy. Repeating NIPT yields a result in greater than 70% of cases. WHAT'S ALREADY KNOWN ABOUT THIS TOPIC?: Fetal fraction (FF) in prenatal cfDNA testing is influenced by maternal and pregnancy factors including body mass index (BMI) and IVF. Low FF has been associated with adverse pregnancy outcomes including fetal aneuploidy and hypertensive diseases of pregnancy. WHAT DOES THIS STUDY ADD?: In a large Irish population, increasing maternal BMI and in-vitro fertilization are the most significant contributors to repeated test failures due to low FF. Greater than 70% of patients with test failure due to low FF will receive a result on 2nd and 3rd NIPT attempts. Patients with no result from NIPT were more likely to undergo diagnostic invasive testing but the risk of aneuploidy was not significantly increased.

Cell-free DNA methylome analysis for early preeclampsia prediction

Preeclampsia (PE) is a leading cause for peripartal morbidity, especially if developing early in gestation. To enable prophylaxis in the prevention of PE, pregnancies at risk of PE must be identified early-in the first trimester. To identify at-risk pregnancies we profiled methylomes of plasma-derived, cell-free DNA from 498 pregnant women, of whom about one-third developed early-onset PE. We detected DNA methylation differences between control and PE pregnancies that enabled risk stratification at PE diagnosis but also presymptomatically, at around 12 weeks of gestation (range 9-14 weeks). The first-trimester risk prediction model was validated in an external cohort collected from two centers (area under the curve (AUC) = 0.75) and integrated with routinely available maternal risk factors (AUC = 0.85). The combined risk score correctly predicted 72% of patients with early-onset PE at 80% specificity. These preliminary results suggest that cell-free DNA methylation profiling is a promising tool for presymptomatic PE risk assessment, and has the potential to improve treatment and follow-up in the obstetric clinic.

Obstetrical, perinatal, and genetic outcomes associated with nonreportable prenatal cell-free DNA screening results

BACKGROUND

The clinical implications of nonreportable cell-free DNA screening results are uncertain, but such results may indicate poor placental implantation in some cases and be associated with adverse obstetrical and perinatal outcomes.

OBJECTIVE

This study aimed to assess the outcomes of pregnancies with nonreportable cell-free DNA screening in a cohort of patients with complete genetic and obstetrical outcomes.

STUDY DESIGN

This was a prespecified secondary analysis of a multicenter prospective observational study of prenatal cell-free DNA screening for fetal aneuploidy and 22q11.2 deletion syndrome. Participants who underwent cell-free DNA screening from April 2015 through January 2019 were offered participation. Obstetrical outcomes and neonatal genetic testing results were collected from 21 primary-care and referral centers in the United States, Europe, and Australia. The primary outcome was risk for adverse obstetrical and perinatal outcomes (aneuploidy, preterm birth at <28, <34, and <37 weeks' gestation, preeclampsia, small for gestational age or birthweight <10th percentile for gestational week, and a composite outcome that included preterm birth at <37 weeks, preeclampsia, small for gestational age, and stillbirth at >20 weeks) after nonreportable cell-free DNA screening because of low fetal fraction or other causes. Multivariable analyses were performed, adjusting for variables known to be associated with obstetrical and perinatal outcomes, nonreportable results, or fetal fraction.

RESULTS

In total, 25,199 pregnant individuals were screened, and 20,194 were enrolled. Genetic confirmation was missing in 1165 (5.8%), 1085 (5.4%) were lost to follow-up, and 93 (0.5%) withdrew; the final study cohort included 17,851 (88.4%) participants who had cell-free DNA, fetal or newborn genetic confirmatory testing, and obstetrical and perinatal outcomes collected. Results were nonreportable in 602 (3.4%) participants. A sample was redrawn and testing attempted again in 427; in 112 (26.2%) participants, results were again nonreportable. Nonreportable results were associated with higher body mass index, chronic hypertension, later gestational age, lower fetal fraction, and Black race. Trisomy 13, 18, or 21 was confirmed in 1.6% with nonreportable tests vs 0.7% with reported results (P=.013). Rates of preterm birth at <28, 34, and 37 weeks, preeclampsia, and the composite outcome were higher among participants with nonreportable results, and further increased among those with a second nonreportable test, whereas the rate of small for gestational age infants was not increased. After adjustment for confounders, the adjusted odds ratios were 2.2 (95% confidence interval, 1.1-4.4) and 2.6 (95% confidence interval, 0.6-10.8) for aneuploidy, and 1.5 (95% confidence interval, 1.2-1.8) and 2.1 (95% confidence interval, 1.4-3.2) for the composite outcome after a first and second nonreportable test, respectively. Of the patients with nonreportable tests, 94.9% had a live birth, as opposed to 98.8% of those with reported test results (adjusted odds ratio for livebirth, 0.20 [95% confidence interval, 0.13-0.30]).

CONCLUSION

Patients with nonreportable cell-free DNA results are at increased risk for a number of adverse outcomes, including aneuploidy, preeclampsia, and preterm birth. They should be offered diagnostic genetic testing, and clinicians should be aware of the increased risk of pregnancy complications.

What helps define outcomes in persistent uninterpretable non-invasive prenatal testing: Maternal factors, fetal fraction or quality scores?

OBJECTIVES

To assess maternal characteristics and comorbidities in patients with persistent uninterpretable non-invasive prenatal testing (NIPT) and to evaluate the association with adverse pregnancy outcome in a general risk population.

METHODS

A retrospective cohort study (July 2017-December 2020) was conducted of patients with persistent uninterpretable NIPT samples. Maternal characteristics and pregnancy outcomes were compared with the general Belgian obstetric population.

RESULTS

Of the 148 patients with persistent uninterpretable NIPT, 37 cases were due to a low fetal fraction (LFF) and 111 due to a low quality score (LQS). Both groups (LFF, LQS) showed more obesity (60.6%, 42.4%), multiple pregnancies (18.9%, 4.5%) and more obstetrical complications. In the LQS group, a high rate of maternal auto-immune disorders (30.6%) was seen and hypertensive complications (17.6%), preterm birth (17.6%) and neonatal intensive care unit (NICU) admission (22%) were significantly increased. In the LFF group hypertensive complications (21.6%), gestational diabetes (20.6%), preterm birth (27%), SGA (25.6%), major congenital malformations (11.4%), c-section rate (51.4%) and NICU admission (34.9%) were significantly increased. Chromosomal abnormalities were not increased in both groups.

CONCLUSIONS

Patients with persistent uninterpretable NIPT have significantly more maternal obesity, comorbidities and adverse pregnancy outcome than the general population and should receive high-risk pregnancy care. Distinguishing between LFF and LQS optimizes counseling because maternal characteristics and pregnancy outcome differ between these groups.

Association between the first and second trimester cell free DNA fetal fraction and spontaneous preterm birth

OBJECTIVE

To evaluate whether the fetal fraction of cell-free DNA at the first and second trimesters is associated with spontaneous preterm birth.

METHODS

This was a retrospective cohort study with singleton pregnancies who underwent noninvasive prenatal testing. According to pregnancy outcome, eligible patients were divided into a delivery group ≥37 weeks of pregnancy (term group) and <37 weeks of pregnancy (spontaneous preterm group). Stepwise linear regression was used to identify maternal characteristics associated with the fetal fraction of cell-free DNA. Logistic regression analysis was performed to evaluate the association between the fetal fraction of cell-free DNA and spontaneous preterm birth, adjusted for confounding factors.

RESULTS

14,020 cases were included in the study, 13292 cases (94.81%) in the term group and 728 cases (5.19%) in the spontaneous preterm group. The cell-free fraction of fetal DNA was inversely correlated with maternal age and body mass index. Positively correlated with gestational age, fertility, and assisted reproductive technology. After adjusting for the covariates, logistic regression analysis revealed no statistically significant association between the fetal fraction of cell-free DNA and spontaneous preterm birth.

CONCLUSION

In our original study, we found no association between the fetal fraction on NIPT and subsequent spontaneous preterm birth.

Use of cell-free signals as biomarkers for early and easy prediction of preeclampsia

Introduction

Preeclampsia (PE) is a leading cause of maternal and perinatal morbidity worldwide. However, current methods of screening are complicated and require special skill sets. In this observational study of prospectively collected samples, we wanted to evaluate if cell-free (cf) DNA could be an efficient biomarker for identification of at-risk patients.

Methods

One hundred patients attending a private prenatal clinic in Canada were enrolled in their first trimester of pregnancy and a blood draw was carried out at 11 + 0 to 14 + 2 weeks' (timepoint A) and 17 + 6 to 25 + 5 weeks of gestation (timepoint B). CfDNA signals, namely concentration, fetal fraction, and fragment size distribution, were correlated with clinical outcomes in the test population to develop the logistic regression model.

Results

Twelve patients developed PE-four early-stage and eight late-stage PE. Significant differences were observed between PE patients and control cases for all three cfDNA signals at timepoint A, while both fetal fraction and concentration were significantly different between PE patients and control cases at timepoint B. Overall, the model had a sensitivity of up to 100% and specificity of up to 87.5% at Timepoint A.

Conclusion

This proof-of-principle study showed that use of this logistic regression model could identify patients at risk of preeclampsia in the first trimester of pregnancy.

Circulating biomarkers associated with placental dysfunction and their utility for predicting fetal growth restriction

Fetal growth restriction (FGR) leading to low birth weight (LBW) is a major cause of neonatal morbidity and mortality worldwide. Normal placental development involves a series of highly regulated processes involving a multitude of hormones, transcription factors, and cell lineages. Failure to achieve this leads to placental dysfunction and related placental diseases such as pre-clampsia and FGR. Early recognition of at-risk pregnancies is important because careful maternal and fetal surveillance can potentially prevent adverse maternal and perinatal outcomes by judicious pregnancy surveillance and careful timing of birth. Given the association between a variety of circulating maternal biomarkers, adverse pregnancy, and perinatal outcomes, screening tests based on these biomarkers, incorporating maternal characteristics, fetal biophysical or circulatory variables have been developed. However, their clinical utility has yet to be proven. Of the current biomarkers, placental growth factor and soluble fms-like tyrosine kinase 1 appear to have the most promise for placental dysfunction and predictive utility for FGR.

Correlation of low fetal fraction of cell-free DNA at the early second-trimester and pregnancy complications related to placental dysfunction in twin pregnancy

Introduction

This study aimed to determine the correlation between fetal fraction (FF) of cell-free DNA (cf-DNA) and pregnancy complications related to placental dysfunction in Twin Pregnancy.

Methods

This retrospective cohort study analyzed twin pregnant women who underwent non-invasive prenatal testing (NIPT) at 12⁺⁰-26⁺⁶ weeks of gestation from April 2017 to April 2021. Low fetal fraction (LFF) was defined individually as less than the 25th, 10th, 5th, and 2.5th percentile among all fetal fractions in the cohort. Primary outcomes included gestational hypertension (GH), preeclampsia (PE), gestational diabetes mellitus (GDM), and small for gestational age (SGA). Logistic regression analysis was used to assess the relationship between LFF and pregnancy complications.

Results

A total of 500 twin pregnancies (male-male twins, 245; female-female twins, 255) were included in this study. In LFF group (FF < 25th percentiles), maternal BMI was significantly higher than FF > 75th percentiles (23.6 kg/m² vs. 21.3 kg/m²; P < 0.001). The risk of SGA increased gradually from FF < 25th percentiles [adjusted odds ratio (OR), 1.71; 95% confidence interval (CI), 1.07-2.99; P = 0.016] to FF < 2.5th percentiles (adjusted OR, 4.44; 95% CI,1.33-14.82; P < 0.015). In addition, the risks of SGA in both fetuses were higher than the risks of at least one fetus SGA in LFF group. LFF had no correlation with GH, PE, and GDM in twin pregnancy.

Conclusion

LFF has a strong association with increased risk of SGA in twin pregnancy. Moreover, FF of cf-DNA may provide a new idea for the early screening of diseases related to placental dysfunction in twin pregnancy.

A comprehensive analysis of the association between placental pathology and recurrent preterm birth

BACKGROUND

Histologic examination of the placenta is often performed after preterm birth. Although placental examination cannot change the index pregnancy outcome, it may inform the risk of adverse outcomes in a subsequent pregnancy. Previous research has examined the association between individual histologic lesions and pregnancy outcomes without consistent results.

OBJECTIVE

This study aimed to determine the independent contributions of the major placental pathology histologic types to recurrent preterm birth.

STUDY DESIGN

This was a retrospective cohort study of deliveries at a tertiary care center from January 2009 to March 2018. Individuals with ≥2 births, an index birth of <37 weeks of gestation, and a placental pathology report from the index pregnancy were included. The presence of maternal vascular malperfusion, fetal vascular malperfusion, acute inflammation, and chronic inflammation was extracted from the pathology reports for each index placenta and classified as none, low grade, or high grade. A log-binomial model incorporating all 4 placental pathology histologic types, index gestational age, race, and maternal age was used to estimate the associations between each placental histologic type and risk of recurrent preterm birth. Moreover, 2-way interaction terms were studied among placental histologic types. In addition, 2 stratified analyses were completed on the basis of characteristics of the index preterm birth: (1) by late preterm (gestational age of 34-36 weeks) vs early-to-moderate preterm birth (<34 weeks) and (2) a subgroup analysis of those with spontaneous preterm birth.

RESULTS

A total of 924 pregnancy pairs met the inclusion criteria. Only high-grade chronic inflammation was independently associated with an increased risk of recurrent preterm birth (adjusted risk ratio, 1.37; 95% confidence interval, 1.03-1.81). Stratified analysis by gestational age group demonstrated maternal vascular malperfusion was associated with recurrent preterm birth only among those with early preterm birth (adjusted risk ratio, 1.40; 95% confidence interval, 1.01-1.93). Among participants with spontaneous preterm labor, no association was found between pathology histologic types and risk of preterm birth.

CONCLUSION

Among index preterm pregnancies, high-grade chronic placental inflammation was associated with recurrent preterm birth. Low-grade maternal vascular malperfusion was associated with recurrent preterm birth only among those with an early or moderate index preterm birth (<34 weeks of gestation). These findings may be useful in determining the risk profile for individual patients and may generate hypotheses as to the pathogenesis of recurrent preterm birth.

Cell-free fetal DNA testing performance and fetal fraction estimation are not affected in ART-conceived pregnancies

STUDY QUESTION

Does ART-based conception influence fetal fraction (FF) estimation and cell-free fetal DNA (cffDNA) testing performance?

SUMMARY ANSWER

Mode of conception (ART versus natural) does not impact FF estimation or cffDNA test informativity rates.

WHAT IS KNOWN ALREADY

Pregnancies achieved via ART are increasing, and cffDNA testing is displacing traditional prenatal screening methods due to its high sensitivity and specificity and noninvasive nature. However, conflicting data exist on cffDNA testing performance and FF in ART pregnancies compared with natural pregnancies.

STUDY DESIGN, SIZE, DURATION

We performed a case-control study that included 21 558 consecutive pregnancies (spontaneous, n = 15 707; ART, n = 5851). ART-conceived pregnancies were stratified into two groups according to oocyte origin. Samples were collected from April 2015 to September 2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study included women from different centers worldwide. Blood samples were drawn from the 10th week of gestation onward. Massive parallel whole-genome sequencing was used to analyze cffDNA content in blood plasma. Two different types of technologies (single-end and paired-end) were applied because of analysis technology changes made by the sequencing provider over time. FF was determined using different methods depending on the type of technology used. Cases with an FF <2% or with failure in any quality control metrics were classified as noninformative. An analysis of covariance model was selected to identify which qualitative (sequencing methodology, mode of conception, type (i.e. multiplicity) of gestation and age (women >35 or <35 years old)) and quantitative (gestational age, BMI) variables were predictors of FF value. Multinomial logistic regression was used to evaluate whether the mode of conception impacted cffDNA testing performance.

MAIN RESULTS AND THE ROLE OF CHANCE

A univariate t-test demonstrated no significant differences in FF values between ART (median FF = 9.2%) and spontaneous pregnancies (median FF = 9.2%). Also, a multivariate analysis showed that the mode of conception, did not strongly impact the percentage of FF. ART-treated women showed a lower incidence of high-risk cffDNA results compared to women who conceived naturally, specifically for trisomy (T)21 (0.7% versus 1.3%, P = 0.001) and T18 (0.1% versus 0.3%, P = 0.001). A multivariate model stratified by type of aneuploidy suggested that these differences were conditioned by oocyte origin, especially for the T21 risk classification (P < 0.0001). False-positive rates (FPRs) were significantly higher in the ART population, mainly for T13 (P = 0.001) and sexual chromosome aneuploidies (SCAs; P < 0.001). A multivariate model suggested that the differences observed in SCAs were caused by sequencing modality rather than by mode of conception. Likewise, ART-treated women who used their own oocytes had a higher probability of a false positive for T13 (P = 0.004).

LIMITATIONS, REASONS FOR CAUTION

Our study lacks follow-up data for low- and high-risk cases of both ART-conceived and naturally conceived pregnancies. Therefore, the results comparing FPR in both populations should be interpreted carefully. Also, collecting information about different ART modalities and regarding preimplantation genetic testing for aneuploidy treatments would help draw definite explanations for the trends observed in this study.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study that demonstrates, with a large sample size, that FF is not influenced by mode of conception, demystifying the notion that patients undergoing ART have a higher probability of noninformative cffDNA testing results. Multivariate models stratified by oocyte origin and type of aneuploidy demonstrated that ART-conceived pregnancies do not have a higher probability of classification as a high-risk pregnancy in prenatal testing. This information is especially valuable to clinicians and genetic counselors when informing patients about the risks and limitations of cffDNA testing in ART pregnancies.

STUDY FUNDING/COMPETING INTEREST(S)

This study was financially supported by Igenomix Lab S.L.U. All authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Non-invasive Prenatal Testing in Pregnancies Following Assisted Reproduction

In the decade since non-invasive prenatal testing (NIPT) was first implemented as a prenatal screening tool, it has gained recognition for its sensitivity and specificity in the detection of common aneuploidies. This review mainly focuses on the emerging role of NIPT in pregnancies following assisted reproductive technology (ART) in the light of current evidence and recommendations. It also deals with the challenges, shortcomings and interpretational difficulties related to NIPT in ART pregnancies, with particular emphasis on twin and vanishing twin pregnancies, which are widely regarded as the Achilles' heel of most pre-natal screening platforms. Future directions for exploration towards improving the performance and extending the scope of NIPT are also addressed.

Hypertensive disorders of pregnancy share common cfDNA methylation profiles

Hypertensive disorders of pregnancy (HDP) contribute substantially to perinatal morbidity and mortality. Epigenetic changes point towards cardio-metabolic dysregulation for these vascular disorders. In early pregnancy, epigenetic changes using cell free DNA (cfDNA) are largely unexplored. We aimed to investigate these in HDP between 11 and 14 weeks of gestation by analysis of cfDNA methylation profiles in patients with hypertensive disorders. We identified patients without chronic hypertension but with subsequent development of preeclampsia (PE) (n = 11), with chronic hypertension (HT) but without PE development (n = 14), and lacking both PE and HT (n = 422). We matched patients according to PE risk factors into three groups (n = 5 each group): (1) PE: no HT but PE development, (2) HT: chronic hypertension but no PE and (3) Control: no PE or HT. We successfully optimized our cfDNA isolation process prior to whole genome bisulfite sequencing. Analysis of cfDNA methylation changes indicate a common predisposition in PE and HT groups, chiefly of maternal origin. Assessment of significant differentially methylated regions and annotated genes point towards a common cardiovascular predisposition in preeclampsia and hypertension groups in the first trimester. We postulate the pivotal role of the maternal cardiovascular system in HDP, which is already evident in the first trimester.

Lower fetal fraction in clinical cell-free DNA screening results is associated with increased risk of hypertensive disorders of pregnancy

OBJECTIVE

To evaluate if fetal fraction (FF) reported on cell-free DNA (cfDNA) screening is a marker for adverse obstetric outcomes.

METHODS

We retrospectively reviewed medical records from a cohort of women with singleton pregnancies who had cfDNA screening. We evaluated if reported FF could predict the following pregnancy complications: hypertensive disorders of pregnancy (HDP), fetal growth restriction, preterm delivery, gestational diabetes mellitus, or a composite maternal morbidity, defined as the presence of at least one of these outcomes.

RESULTS

Receiver operating curve analysis was performed on FF from 534 women to define the FF that differentiated a low FF group (<10%; N = 259) and a high FF group (≥10%; N = 275). Hypertensive disorders of pregnancy were more common for women in the low FF group (32.0% vs. 11.6% and p < 0.001), who had a two-fold odds of developing HDP (p = 0.006). Composite maternal morbidity was also more common for women in the low FF group (51.4% vs. 30.2% and p < 0.001), who had a 1.7-fold odds of developing any of the adverse obstetrical outcomes (p = 0.014).

CONCLUSION

We found that low FF on cfDNA screening is associated with an increased risk of HDP. Fetal fraction reported that cfDNA screening reports have potential as a predictive marker for the development of HDP and adverse outcomes.

Association of fetal fraction with hypertensive disorders of pregnancy incidence and disease severity

BACKGROUND

Hypertensive disorders of pregnancy contribute to maternal and offspring morbidity and mortality. Studies suggest that a lower early pregnancy fetal fraction is associated with an increased risk of hypertensive disorders of pregnancy. However, maternal obesity significantly affects fetal fraction and is a risk factor for hypertensive disorders of pregnancy.

OBJECTIVE

We determined the association between fetal fraction (using a standardized single-institution platform, including male and female fetuses) and hypertensive disorders of pregnancy, stratified by obesity status. Second, we evaluated differences in total cell-free DNA concentration and correlation of fetal fraction with clinical markers of hypertensive disorders of pregnancy severity.

STUDY DESIGN

This was a retrospective, single-institution study of a previously validated cell-free DNA-based noninvasive prenatal screening assay of 1058 samples. Maternal body mass index at the time of noninvasive prenatal screening was assessed, and hypertensive disorders of pregnancy were confirmed by a detailed medical record review. Differences in fetal fraction and total cell-free DNA concentration between the groups were assessed with univariate analyses. Multivariable regression was used to evaluate the association between fetal fraction and hypertensive disorders of pregnancy, adjusted for body mass index, maternal age, gestational age at noninvasive prenatal screening, and fetal sex. The association between fetal fraction and hypertensive disorders of pregnancy among individuals with obesity (body mass index, ≥30 kg/m2) and individuals without obesity (body mass index, <30 kg/m2) was investigated while controlling for the aforementioned covariates. Lastly, multivariable linear regression was used to evaluate the association between fetal fraction and clinical markers of hypertensive disorders of pregnancy severity.

RESULTS

We identified individuals with (n=117) and without (n=941) hypertensive disorders of pregnancy with noninvasive prenatal screening drawn before 20 weeks of gestation and with fetal fraction and body mass index data available. Those with hypertensive disorders of pregnancy had a lower fetal fraction (10.2%±4.2% vs 11.6%±4.7%; P<.01), without differences in total cell-free DNA concentration (P=.14). When groups were stratified by obesity status, this relationship was only valid for individuals without obesity (P=.02). Only when logistic regression analysis was restricted to individuals without obesity did the likelihood of hypertensive disorders of pregnancy rise with decreasing fetal fraction (odds ratio, 0.93; 95% confidence interval, 0.88-0.99; P=.02). In addition, fetal fraction was inversely associated with maximum systolic blood pressure at the time of hypertensive disorders of pregnancy only in the population without obesity (β, -0.08; 95% confidence interval, -0.147 to -0.01; P=.02).

CONCLUSION

Although a lower fetal fraction is associated with the development of hypertensive disorders of pregnancy, the use of this parameter for the prediction may be problematic in individuals with obesity, as obesity has such a profound effect on fetal fraction. However, we uniquely noted that among individuals without obesity, fetal fraction is lower for those that develop hypertensive disorders of pregnancy and lower fetal fraction increases the odds of hypertensive disorders of pregnancy development. Lastly, low fetal fraction in the population without obesity that developed hypertensive disorders of pregnancy was associated with higher systolic blood pressure at the time of hypertensive disorders of pregnancy, an important clinical marker of hypertensive disorders of pregnancy severity. As analytical approaches of cell-free DNA interrogation advance, the prediction of placental-mediated disorders with first-trimester sampling is likely to improve, although this may remain challenging in gravidas with obesity, a cohort at high risk of developing hypertensive disorders of pregnancy.

Low Fetal Fraction of Cell Free DNA at Non-Invasive Prenatal Screening Increases the Subsequent Risk of Preterm Birth in Uncomplicated Singleton Pregnancy

Objective

To examine the association between low fetal fraction (FF) of cell free DNA determined at non-invasive prenatal screening (NIPS) and the subsequent risk of preterm birth in uncomplicated singleton pregnancy.

Methods

We retrospectively interrogated NIPS System and hospitalization records from April 2018 to August 2019 and obtained results from 1521 consecutive and uncomplicated women with singleton pregnancy in which plasma FF of cell free DNA at NIPS had been investigated together with birth outcomes. We examined the association between FF and preterm birth (PTB) by regression analysis.

Results

The incidence of preterm birth, low birthweight, and macrosomia in the study population was 5.06%, 2.89%, and 7.17%, respectively. FF at NIPS in the second to fourth quartiles (8.40-11.07, 11.08-13.70, and >13.70%, respectively) was associated with higher gestational age at delivery relative to the lowest quartile (<8.40%), with estimated mean increases of 0.27 weeks (95% CI: 0.05-0.49), 0.29 weeks (95% CI: 0.06-0.51), and 0.28 weeks (95% CI: 0.05-0.51), respectively (P for trend = 0.027). Low FF (< the 5^th percentile) was associated with an increased risk of PTB (adjusted OR: 2.23, 95% CI: 1.01-4.98, P = 0.047) compared to normal FF (≥ the 5^th and ≤ the 95^th percentiles). In addition, when compared to women with normal FF and body mass index (BMI) <25 at NIPS, the risk of early PTB (< 34 weeks gestation) was remarkably significantly higher among those with low FF and BMI ≥25 (adjusted OR: 6.29, 95% CI: 1.71-23.15, P = 0.006).

Conclusion

Our study supports the association of low FF at NIPS with PTB (especially early PTB) for uncomplicated singleton pregnancy.

The low fetal fraction at the first trimester is associated with adverse pregnancy outcomes in IVF singleton pregnancies with single embryo transfer from frozen cycles

PURPOSE

To study the associations between fetal fraction at the first trimester and subsequent adverse pregnancy outcomes (APOs) in IVF singleton pregnancies with single embryo transfer from frozen cycles.

METHODS

This is a single-center retrospective cohort study on IVF singleton pregnancies with single embryo transfer from frozen cycles. A total of 8457 women were collected between March 2015 and September 2018 from the Center for Reproductive Medicine, Shandong University, China. Participants underwent cell-free DNA (cfDNA) sequencing at 11-13 weeks' gestation. Multivariable logistic regressions were performed with the risk of APOs based on various predictor variables.

RESULTS

A total of 8457 women were included in the analysis of which 1563 (18.48%) women developed one or more APOs. The hypertensive disorders of pregnancy (HDP) (N = 515), gestational diabetes mellitus (GDM) (N = 684), preterm birth (PTB) (N = 567), and low birth weight (LBW) (N = 306) groups had lower fetal fraction compared with the no pregnancy complication (NPC) group (all p values < 0.05). Based on the multivariable logistic regression results, the optimal cutoff values of fetal fraction were 9.30%, 12.54%, 9.10%, 12.65%, and 13.83% for at least one APO, HDP, GDM, PTB, and LBW, respectively. After adjustment for potential maternal confounders, women in the low fetal fraction (LFF) group had a higher risk for the APOs compared with high fetal fraction (HFF) group.

CONCLUSIONS

The fetal fraction in HDP, GDM, PTB, and LBW groups were lower than NPC group in IVF singleton pregnancies with single embryo transfer from frozen cycles in China.

Droplet Digital PCR for Non-Invasive Prenatal Detection of Fetal Single-Gene Point Mutations in Maternal Plasma

Non-invasive prenatal testing (NIPT) is based on the detection and characterization of circulating cell-free fetal DNA (ccffDNA) in maternal plasma and aims to identify genetic abnormalities. At present, commercial NIPT kits can detect only aneuploidies, small deletions and insertions and some paternally inherited single-gene point mutations causing genetic diseases, but not maternally inherited ones. In this work, we have developed two NIPT assays, based on the innovative and sensitive droplet digital PCR (ddPCR) technology, to identify the two most common β thalassemia mutations in the Mediterranean area (β⁺IVSI-110 and β⁰39), maternally and/or paternally inherited, by fetal genotyping. The assays were optimized in terms of amplification efficiency and hybridization specificity, using mixtures of two genomic DNAs with different genotypes and percentages to simulate fetal and maternal circulating cell-free DNA (ccfDNA) at various gestational weeks. The two ddPCR assays were then applied to determine the fetal genotype from 52 maternal plasma samples at different gestational ages. The diagnostic outcomes were confirmed for all the samples by DNA sequencing. In the case of mutations inherited from the mother or from both parents, a precise dosage of normal and mutated alleles was required to determine the fetal genotype. In particular, we identified two diagnostic ranges for allelic ratio values statistically distinct and not overlapping, allowing correct fetal genotype determinations for almost all the analyzed samples. In conclusion, we have developed a simple and sensitive diagnostic tool, based on ddPCR, for the NIPT of β⁺IVSI-110 and β⁰39 mutations paternally and, for the first time, maternally inherited, a tool, which may be applied to other single point mutations causing monogenic diseases.

Factors Affecting the Fetal Fraction in Noninvasive Prenatal Screening: A Review

A paradigm shift in noninvasive prenatal screening has been made with the discovery of cell-free fetal DNA in maternal plasma. Noninvasive prenatal screening is primarily used to screen for fetal aneuploidies, and has been used globally. Fetal fraction, an important parameter in the analysis of noninvasive prenatal screening results, is the proportion of fetal cell-free DNA present in the total maternal plasma cell-free DNA. It combines biological factors and bioinformatics algorithms to interpret noninvasive prenatal screening results and is an integral part of quality control. Maternal and fetal factors may influence fetal fraction. To date, there is no broad consensus on the factors that affect fetal fraction. There are many different approaches to evaluate this parameter, each with its advantages and disadvantages. Different fetal fraction calculation methods may be used in different testing platforms or laboratories. This review includes numerous publications that focused on the understanding of the significance, influencing factors, and interpretation of fetal fraction to provide a deeper understanding of this parameter.

Low fetal fraction in cell-free DNA testing is associated with adverse pregnancy outcome: Analysis of a subcohort of the TRIDENT-2 study

Objectives

To assess the association between low fetal fraction (FF) in prenatal cell‐free DNA (cfDNA) testing and adverse pregnancy outcomes.

Methods

We conducted a retrospective cohort study of participants of the TRIDENT‐2 study (Dutch nationwide government‐supported study offering cfDNA screening for fetal aneuploidies) who received a failed test result due to low FF (<4%) between April 2017 until February 2018. Outcome measures included pregnancy‐induced hypertension (PIH), pre‐eclampsia (PE), small for gestational age neonates (SGA), spontaneous preterm birth (sPTB), gestational diabetes mellitus (GDM), chromosomal aberrations, and congenital structural anomalies.

Results

Test failure due to low FF occurred in 295 women (1.12% of tests performed). Information regarding pregnancy outcomes was available for 96.3% of these women. The incidence of PIH, PE, SGA, sPTB, and GDM was 11.2%, 4.1%, 7.3%, 5.1%, and 14.8%, respectively. The prevalence of chromosomal aberrations and congenital structural anomalies was 1.4% and 4.1%, respectively. Incidences of PIH, PE ≥ 34 weeks of gestation, GDM, and prevalence of aneuploidy and congenital structural anomalies were higher in women with low FF compared to the general Dutch obstetric population.

Conclusion

Low FF is associated with adverse pregnancy outcomes. The value of FF in the prediction of these outcomes needs to be further established.

Association between low fetal fraction and hypertensive disorders of pregnancy in in vitro fertilization-conceived pregnancies

BACKGROUND

Fetal fraction from noninvasive prenatal screening has been used as a predictive marker for hypertensive disorders of pregnancy in spontaneous pregnancies.

OBJECTIVE

We aimed to determine whether fetal fraction from noninvasive prenatal screening predicts hypertensive disorders of pregnancy in pregnancies conceived by assisted reproductive technology, stratified by fresh and frozen embryo transfer.

STUDY DESIGN

Retrospective cohort study of women with singleton pregnancies who underwent fresh or frozen embryo transfer, had noninvasive prenatal screening, and had a live birth >20 weeks at a single institution from 2013 to 2019. Women with major anomalies, nonreportable noninvasive prenatal screening, or chronic hypertension were excluded. Fetal fraction was corrected for gestational age, noninvasive prenatal screening platform, and defined as low if it is less than fifth percentile for the study population. The primary outcome was hypertensive disorders of pregnancy during delivery hospitalization, stratified by fresh vs frozen embryo transfer. We performed multivariable logistic regression analyses to determine whether low fetal fraction predicts hypertensive disorders of pregnancy for fresh and frozen embryo transfer, controlling for age, prepregnancy body mass index, heparin use, low-dose aspirin use, estradiol level if fresh embryo transfer, and trophectoderm biopsy and cycle type if frozen embryo transfer.

RESULTS

We included 81 women with low fetal fraction and 847 women with normal fetal fraction. The adjusted prevalence of hypertensive disorders of pregnancy in women with low fetal fraction was 24.9% in fresh embryo transfer and 34.5% in frozen embryo transfer. In fresh embryo transfer pregnancies, the odds of hypertensive disorders of pregnancy were higher among women with low fetal fraction (adjusted odds ratio, 2.46; 95% confidence interval, 1.07-5.30; P=.026). In frozen embryo transfer pregnancies, there was no association between low fetal fraction and hypertensive disorders of pregnancy (adjusted odds ratio, 1.43; 95% confidence interval, 0.69-2.88; P=.321).

CONCLUSION

Low fetal fraction is associated with hypertensive disorders of pregnancy in women who conceive by fresh embryo transfer. Fetal fraction may represent a clinically useful marker for screening for hypertension and allow clinicians to target risk reduction strategies, such as low-dose aspirin, in pregnancies conceived by fresh embryo transfer.

Association between low fetal fraction in cell-free DNA testing and adverse pregnancy outcome: A systematic review

Objective

Low fetal fraction (LFF) in prenatal cell‐free DNA (cfDNA) testing is an important cause of test failure and no‐call results. LFF might reflect early abnormal placentation and therefore be associated with adverse pregnancy outcome. Here, we review the available literature on the relationship between LFF in cfDNA testing and adverse pregnancy outcome.

Method

A systematic literature search was conducted in MEDLINE and EMBASE up to November 1, 2020.

Results

Five studies met the criteria for inclusion; all were retrospective observational cohort studies. The cohort sizes ranged from 370 to 6375 pregnancies, with all tests performed in the first trimester or early second trimester. A 4% cutoff for LFF was used in two studies, two studies used the 5th and 25th percentiles, respectively, and one study used a variety of cutoff values for LFF. LFF in prenatal cfDNA testing was observed to be associated with hypertensive disease of pregnancy, small for gestational age neonates, and preterm birth. Conflicting results were found regarding the association between LFF and gestational diabetes mellitus.

Conclusions

LFF in cfDNA testing is associated with adverse pregnancy outcome,specifically pregnancy‐related hypertensive disorders, preterm birth, and impaired fetal growth related to placental dysfunction. Since the available evidence is limited, a large prospective cohort study on the relationship between fetal fraction and pregnancy outcomes is needed.

What's already known about this topic?

Low fetal fraction (LFF) in prenatal cell‐free DNA (cfDNA) testing is an important cause of test failure and no‐call results and has been associated with aneuploidy

LFF might also reflect early abnormal placentation and therefore be associated with adverse pregnancy outcome

What does this review add?

This review summarizes the available data on LFF in prenatal cfDNA testing and its relation to adverse pregnancy outcomes

LFF was found to be associated with pregnancy‐related hypertensive disorders, preterm birth, and impaired fetal growth related to placental dysfunction

Since the available evidence is limited, a large prospective cohort study on the relationship between fetal fraction and pregnancy outcomes is needed

Low fetal fraction in obese women at first trimester cell-free DNA based prenatal screening is not accompanied by differences in total cell-free DNA

OBJECTIVE

Reasons for first trimester noninvasive prenatal screening (NIPS) test failure in obese women remain elusive. As dilution from maternal sources may be explanatory, we determined the relationship between obesity, fetal fraction (FF), and total cell-free DNA (cfDNA) using our NIPS platform.

METHODS

We assessed differences in first trimester (≤14 weeks) FF, indeterminate rate, and total cfDNA between obese (n = 518) and normal-weight women (n = 237) after exclusion of confounders (anticoagulation, autoimmunity, aneuploidy) and controlling for covariates.

RESULTS

Fetal fraction was lower, and the indeterminate rate higher, in obese compared to controls (9.2% ± 4.4 vs. 12.5% ± 4.5, p < 0.001 and 8.4 vs. 1.7%, p < 0.001, respectively), but total cfDNA was not different (92.0 vs. 82.1 pg/µl, p = 0.10). For each week, the FF remained lower in obese women (all p < 0.01) but did not increase across the first trimester for either group. Obesity increased the likelihood of indeterminate result (OR 6.1, 95% CI 2.5, 14.8; p < 0.001) and maternal body mass index correlated with FF (β -0.27, 95% CI -0.3, -0.22; p < 0.001), but not with total cfDNA (β 0.49, 95% CI -0.55, 1.53; p = 0.3).

CONCLUSIONS

First trimester obese women have persistently low FF and higher indeterminate rates, without differences in total cfDNA, suggesting placental-specific mechanisms versus dilution from maternal sources as a potential etiology.

Circulating Nucleic Acids in Maternal Plasma and Serum in Pregnancy Complications: Are They Really Useful in Clinical Practice? A Systematic Review

OBJECTIVE

A systematic review was carried out to summarize the available evidence to assess whether circulating nucleic acids in maternal plasma and serum (CNAPS) have the potential to serve as extra and independent markers for the prediction and/or progression monitoring of the most common and severe complications of pregnancy, including preeclampsia, intrauterine growth restriction, preterm delivery, morbidly adherent placenta, gestational diabetes, antiphospholipid syndrome, threatened abortion, intrahepatic cholestasis of pregnancy, and hyperemesis gravidarum.

METHOD

A comprehensive literature search of the MEDLINE (PubMed), EMBASE, and ISI Web of Knowledge databases was conducted to identify relevant studies that included amounts of CNAPS in the abovementioned pregnancy complications.

RESULTS

Eighty-three studies met the eligibility criteria. The vast majority of studies were conducted on the quantity of total circulating cell free DNA (cfDNA) and cell free fetal DNA (cffDNA), and some were conducted on messenger RNA (mRNA) species. A few studies have instead evaluated the cell free DNA fetal fraction (cfDNAff), but only in a limited number of pregnancy complications. Despite the growing interest and the abundance of the papers available, little information is available for other new CNAPS, including microRNA (miRNA), long noncoding RNA (lncRNA), mitochondrial DNA (mtDNA), and circular RNA.

CONCLUSION

Due to the heterogeneity of the populations enrolled, the scarcity of the studies that adjusted the CNAPS values for possible confounding factors, and the difficulty in interpreting the published data, no conclusion regarding the statistical robustness and clinical relevance of the data can be made at present. If assayed at the third trimester, the CNAPS have, however, shown better performance, and could be used in populations already at risk of developing complications as suggested by the presence of other clinical features. Other CNAPS, including miRNA, are under investigation, especially for the screening of gestational diabetes mellitus, but no data about their clinical utility are available. Circulating DNA (cfDNA, cffDNA, and cfDNAff) and mRNA have not been properly evaluated yet, especially in patients asymptomatic early in pregnancy but who developed complications later, perhaps because of the high cost of these techniques and the availability of other predictors of pregnancy complications (biochemical, biophysical, and ultrasound markers). Therefore, from the analysis of the data, the positive predictive value is not available. As regards the new CNAPS, including miRNA, there are still no sufficient data to understand if they can be promising markers for pregnancy complications monitoring and screening, since CNAPS are statistically weak and expensive. It is reasonable to currently conclude that the use of the CNAPS in clinical practice is not recommended.

Fetal fraction of cell-free DNA in pregnancies after fresh or frozen embryo transfer following assisted reproductive technologies

STUDY QUESTION

Is the fetal fraction (FF) of circulating cell-free DNA (cfDNA) affected in pregnancies following ART treatment with either fresh or frozen embryo transfer (ET) compared with natural conception?

SUMMARY ANSWER

This study shows a significant reduction in the FF in ART patients compared with naturally conceived pregnancies, which seems to be more pronounced after fresh ET compared with frozen ET.

WHAT IS KNOWN ALREADY

Non-invasive prenatal testing (NIPT) is based on cfDNA in maternal blood, of which about 10% is of placental origin and thus represents the fetal karyotype. Validation studies have demonstrated a high sensitivity, specificity and positive predictive value of NIPT for the detection of fetal trisomy 21, 18 and 13. Nevertheless, the FF of cfDNA is an important factor for NIPT test accuracy. Several studies have found a reduction in FF for pregnancies following ART in comparison with natural conception. However, knowledge on how the FF is affected in ART pregnancies after fresh ET compared with frozen ET is very limited.

STUDY DESIGN, SIZE, DURATION

The study was designed as a case-control study. A total of 54 women with an ongoing pregnancy following ART treatment were included. After exclusion for different reasons, statistical analyses were based on 23 NIPT samples from pregnant women treated with fresh ET and 26 NIPT samples from pregnant women treated with frozen-thawed ET in a modified natural cycle. Women were included between February 2018 and November 2018. The results were compared with a control group of 238 naturally conceived pregnancies with a high-risk result from the combined first trimester screening (cFTS).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study included women from the Fertility Clinics at Copenhagen University Hospital Hvidovre and Copenhagen University Hospital Rigshospitalet. Blood samples for NIPT analysis were drawn between 11 + 0 and 14 + 2 weeks of gestation and were all analyzed at the NIPT Center at Copenhagen University Hospital Hvidovre. The NIPT-test was performed by massive-parallel whole-genome sequencing. The FF was determined using the SeqFF algorithm.

MAIN RESULTS AND THE ROLE OF CHANCE

We found a reduction in FF in ART patients compared with naturally conceived pregnancies, and the reduction was more pronounced for ART pregnancies after fresh ET (mean FF = 0.049) compared with frozen ET (mean FF = 0.063) (multivariate analysis adjusted for maternal BMI, P = 0.02). Another multivariate analysis, adjusted for BMI and multiples of median (MoM) values for pregnancy-associated plasma protein-A (PAPP-A), demonstrated a significantly reduced FF for ART pregnancies (mean FF = 0.056) compared with naturally conceived pregnancies (mean FF = 0.072) (P < 0.0001). We found that FF was significantly reduced with increasing maternal BMI (P < 0.0001) and with decreasing MoM values of PAPP-A (P = 0.003).

LIMITATIONS, REASONS FOR CAUTION

A limitation of our study design was the relatively small sample size. Another limitation was that the control group was not matched with the ART-treated women. The majority of the women from the control group had a high risk from cFTS, thereby their biochemical markers were diverging. However, the biochemical markers for the ART-treated women with fresh or frozen ET were not divergent within the subgroups.

WIDER IMPLICATIONS OF THE FINDINGS

Concurrent with other studies demonstrating a reduced FF for singleton pregnancies after ART treatment compared with naturally conceived pregnancies, we found a reduction in FF between the two groups. This is one of the first studies to examine FF in ART pregnancies after fresh ET compared with frozen ET, hence the existing knowledge is limited. We find that FF is even more reduced in pregnancies following fresh ET compared with frozen ET, which might possibly reflect the predisposition of being small for gestational age after fresh ET compared with natural cycle frozen ET.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by the A.P. Møller og Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal (the A.P. Møller Foundation for General Purposes). All authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

NA.

Noninvasive inferring expressed genes and in vivo monitoring of the physiology and pathology of pregnancy using cell-free DNA

BACKGROUND

Noninvasive monitoring of fetal development and the early detection of pregnancy-associated complications is challenging, largely because of the lack of information about the molecular spectrum during pregnancy. Recently, cell-free DNA in plasma was found to reflect the global nucleosome footprint and status of gene expression and showed potential for noninvasive health monitoring during pregnancy.

OBJECTIVE

We aimed to test the relationships between plasma cell-free DNA profiles and pregnancy biology and evaluate the use of a cell-free DNA profile as a noninvasive method for physiological and pathologic status monitoring during pregnancy.

STUDY DESIGN

We used genome cell-free DNA sequencing data generated from noninvasive prenatal testing in a total of 2937 pregnant women. For each physiological and pathologic condition, features of the cell-free DNA profile were identified using the discovery cohort, and support vector machine classifiers were built and evaluated using independent training and validation cohorts.

RESULTS

We established nucleosome occupancy profiles at transcription start sites in different gestational trimesters, demonstrated the relationships between gene expression and cell-free DNA coverage at transcription start sites, and showed that the cell-free DNA profiles at transcription start sites represented the biological processes of pregnancy. In addition, using cell-free DNA data, nucleosome profiles of transcription factor binding sites were identified to reflect the transcription factor footprint, which may help to reveal the molecular mechanisms underlying pregnancy. Finally, by using machine-learning models on low-coverage noninvasive prenatal testing data, we evaluated the use of cell-free DNA nucleosome profiles for distinguishing gestational trimesters, fetal sex, and fetal trisomy 21 and highlighted its potential utility for predicting physiological and pathologic fetal conditions by using low-coverage noninvasive prenatal testing data.

CONCLUSION

Our analyses profiled nucleosome footprints and regulatory networks during pregnancy and established a noninvasive proof-of-principle methodology for health monitoring during pregnancy.

Fetal fraction of cell free DNA in screening for hypertensive disorders at 11-13 weeks

OBJECTIVE

To investigate whether first-trimester maternal plasma fetal fraction is altered in women that subsequently develop preeclampsia (PE) or gestational hypertension (GH) and to examine its potential value in improving the performance of screening for PE and GH by maternal factors and maternal serum pregnancy associated plasma protein-A (PAPP-A), mean arterial pressure (MAP) and uterine artery pulsatility index (UtA-PI).

METHODS

The study population of 10,131 pregnancies undergoing cell free fetal DNA testing at 11-13 weeks' gestation included 91 (0.9%) cases with preterm-PE, 222 (2.2%) cases with term-PE, 360 (3.6%) with GH and 9,458 (93.4%) cases unaffected by hypertensive disorders. Maternal plasma fetal fraction levels were expressed as multiples of the median (MoM) after adjustment for maternal factors and crown-rump length. The performance of screening for preterm-PE, term PE and GH by maternal factors and MoM values of fetal fraction, PAPP-A, UtA-PI and MAP was evaluated by receiver operating characteristic (ROC) curves.

RESULTS

The median fetal fraction MoM was significantly lower in the preterm-PE (0.825; IQR 0.689-1.115 MoM, p < .001), term-PE (0.946; IQR 0.728-1.211 MoM, p = .028) and GH (0.928; IQR 0.711-1.182 MoM, p < .001) groups than in the unaffected group (1.002; IQR 0.785-1.251 MoM). However, the performance of screening for PE or GH by maternal factors alone or by maternal factors and PAPP-A, UtA-PI and MAP was not significantly improved by the addition of fetal fraction.

CONCLUSIONS

First trimester maternal plasma fetal fraction is not useful in screening for hypertensive disorders of pregnancy.

Implications of non-invasive prenatal testing for identifying and managing high-risk pregnancies

Non-invasive prenatal testing is regularly used to screen for aneuploidies and Rhesus status of a fetus. Since 1997 when free fetal DNA (ffDNA) in the maternal circulation was first identified, it has been hypothesized that it may be possible to use non-invasive prenatal testing (NIPT) to identify high-risk pregnancies including pre-eclampsia, growth restriction and preterm birth. Since then there has been much interest in this area as a way to identify and understand disease processes. This review presents the current evidence for this approach. For pre-eclampsia the hypothesis is that ffDNA would increase but the evidence for this is heterogenous across studies and trimesters. There is however increasing agreement between studies that by the third trimester ffDNA is more likely to be raised in pre-eclamptic patients than controls. For preterm birth, again, the main hypothesis is that ffDNA should increase. The results are also heterogenous, with some studies finding increased ffDNA prior to preterm birth, and others finding no change. For fetal growth restriction, there are competing theories for reduced and increased ffDNA and some studies suggest that levels are raised and some reduced. There are complexities in interpreting all of this evidence as the studies' designs, patient populations, and especially in the context of growth restriction, the definitions are not clear. Furthermore, authors use different biochemical tests and different units to describe their results, making meta-analysis difficult. All of these issues and conflicting findings lead us to the conclusion that currently there is yet no definitive place in clinical practice for NIPT to support the diagnosis and management of high-risk pregnancies. However, it is vital that this research continues as it could open the door to better understanding of the disease process and novel approaches to management.

Association between low fetal fraction of cell free DNA at the early second-trimester and adverse pregnancy outcomes

OBJECTIVE

The purpose of this study was to examine whether low fetal fraction (FF) of cell free DNA is associated with risks of adverse pregnancy outcomes.

METHODS

This was a historical cohort study of 2191 women with singleton pregnancies who had non-invasive prenatal test (NIPT) at 13 to 26 weeks of gestation. Data were collected from prenatal screening system and hospital records. Main outcome was the subsequent diagnosis of gestational diabetes mellitus (GDM), intrahepatic cholestasis of pregnancy (ICP), preeclampsia (PE), pregnancy induced hypertension (PIH) and preterm birth (PTB). Logistic regression analysis was performed to evaluate the association between LFF and adverse pregnancy outcomes.

RESULTS

The prevalence of GDM, ICP, PE, PIH and PTB was 23.87% (523), 4.02% (88), 2.92% (64), 2.83% (62) and 6.85% (150), respectively. Low FF, defined as less than the 10th percentile, was associated with an increased risk of PE (adjusted OR = 2.06, 95% CI: 1.07-3.98) and early PTB (<34 weeks' gestation: adjusted OR = 3.09, 95% CI: 1.21-7.92). In addition, low FF, defined as less than the 5th percentile, was associated with an increased risk of low birth weight babies (<2500 g: adjusted OR = 2.50, 95% CI: 1.01-6.17). However, there was no significant association between low FF and GDM, as well as ICP and PIH.

CONCLUSION

Our study provides evidence that low FF is associated with PE and early PTB. Further exploration of the clinical significance of low FF is warranted.

Maternal total cell-free DNA in preeclampsia with and without intrauterine growth restriction

Elevation of total cell-free DNA (cfDNA) in patients with preeclampsia is well-known; however, whether this change precedes the onset of symptoms remains inconclusive. Here, we conducted a nested case-control study to determine the elevation of cfDNA levels in women who subsequently developed preeclampsia. Methylated HYP2 (m-HYP2) levels were determined in 68 blood samples collected from women with hypertensive disorders of pregnancy, along with 136 control samples, using real-time quantitative PCR. The measured m-HYP2 levels were converted to multiples of the median (MoM) values for correction of maternal characteristics. The m-HYP2 levels and MoM values in patients with preeclampsia were significantly higher than in controls during the third trimester (P < 0.001, both), whereas those for women who subsequently developed preeclampsia did not differ during the second trimester. However, when patients with preeclampsia were divided based on the onset-time of preeclampsia or 10th percentile birth weight, both values were significantly higher in women who subsequently developed early-onset preeclampsia (P < 0.05, both) and preeclampsia with small-for-gestational-age (SGA) neonate (P < 0.01, both) than controls. These results suggested that total cfDNA levels could be used to predict early-onset preeclampsia or preeclampsia with SGA neonate.

Total Versus Free Placental Growth Factor Levels in the Pathogenesis of Preeclampsia

Elevated circulating sFLT-1 (soluble fms-like tyrosine kinase) and low levels of its ligand, PlGF (placental growth factor), are key characteristics of preeclampsia. However, it is unclear if the low levels of plasma PlGF noted during preeclampsia are due to decreased placental production of PlGF or due to binding of PlGF by increased circulating sFLT-1. Here, we describe a biochemical procedure to dissociate PlGF-sFLT-1 complex ex vivo and when used in conjunction with an immunoassay platform, demonstrate a method to measure total and free PlGF in human blood samples. Using this method, we noted that plasma free PlGF levels were significantly lower in preeclampsia (N=22) than in nonhypertensive controls (N=24; mean, 314 versus 686 pg/mL, P<0.05), but total PlGF levels were not different (mean, 822 versus 800 pg/mL, P=0.49). In contrast, total sFLT-1 levels were significantly higher in preeclampsia than in nonhypertensive controls (mean, 16 957 versus 3029 pg/mL, P<0.01) and sFLT-1 levels correlated with bound PlGF levels (bound PlGF=total PlGF-free PlGF) in these samples (r²=0.68). We confirmed these findings in an independent cohort of subjects (N=49). Furthermore, we did not detect any difference in PlGF mRNA by quantitative polymerase chain reaction or in PlGF protein expression by immunohistochemistry in preeclamptic placentas when compared with nonhypertensive controls. In contrast, sFLT-1 mRNA and protein levels were upregulated in placentas from women with preeclampsia. Taken together with prior studies, our results provide evidence that decrease in circulating PlGF noted during preeclampsia is largely mediated by excess circulating sFLT-1.

Biochemical parameters, dynamic tensiometry and circulating nucleic acids for cattle blood analysis: a review

The animal’s blood is the most complicated and important biological liquid for veterinary medicine. In addition to standard methods that are always in use, recent technologies such as dynamic tensiometry (DT) of blood serum and PCR analysis of particular markers are in progress. The standard and modern biochemical tests are commonly used for general screening and, finally, complete diagnosis of animal health. Interpretation of major biochemical parameters is similar across animal species, but there are a few peculiarities in each case, especially well-known for cattle. The following directions are discussed here: hematological indicators; “total protein” and its fractions; some enzymes; major low-molecular metabolites (glucose, lipids, bilirubin, etc.); cations and anions. As example, the numerous correlations between DT data and biochemical parameters of cattle serum have been obtained and discussed. Changes in the cell-free nucleic acids (cfDNA) circulating in the blood have been studied and analyzed in a variety of conditions; for example, pregnancy, infectious and chronic diseases, and cancer. CfDNA can easily be detected using standard molecular biological techniques like DNA amplification and next-generation sequencing. The application of digital PCR even allows exact quantification of copy number variations which are for example important in prenatal diagnosis of chromosomal aberrations.

Can fetal fractions in the cell-free DNA test predict the onset of fetal growth restriction?

Objective To investigate the possible predictive value of fetal fraction in the cell-free DNA (cfDNA) test in pregnancies with early- and late-onset fetal growth restriction (FGR). Methods This retrospective study comprised 247 women who were screened using the cfDNA test for aneuploidies during the first or second trimester and had deliveries at our institution from January 2016 to December 2019. The fetal fractions of women with early- (n = 14) and late-onset (n = 83) FGR and those with uncomplicated pregnancies (n = 150) were compared. Results The median fetal fractions for the early-onset FGR, late-onset FGR, and control groups were 5.7 [interquartile range (IQR) 2.65], 7 (IQR 5), and 7.35 (IQR 3.65), respectively. The fetal fractions were significantly lower in the early-onset FGR group than in the late-onset FGR and control groups (P = 0.047 and P = 0.037, respectively). There was no difference in fetal fractions between the late-onset FGR and control groups (P = 1.00). Conclusion As a placenta-related disease, early-onset FGR had lower fetal fractions in the cfDNA test than uncomplicated pregnancies. For clinical use, lower fetal fractions can contribute as a biomarker for screening asymptomatic women for possible placenta-related diseases, such as early-onset FGR. However, more studies are needed to define the "lower" limit.

Cell-Free Fetal DNA Increases Prior to Labor at Term and in a Subset of Preterm Births

Cell-free fetal DNA in the maternal circulation has been associated with the onset of labor at term. Moreover, clinical studies have suggested that cell-free fetal DNA has value to predict pregnancy complications such as spontaneous preterm labor leading to preterm birth. However, a mechanistic link between cell-free fetal DNA and preterm labor and birth has not been established. Herein, using an allogeneic mouse model in which a paternal green fluorescent protein (GFP) can be tracked in the fetuses, we established that cell-free fetal DNA (Egfp) concentrations were higher in late gestation compared to mid-pregnancy and were maintained at increased levels during the onset of labor at term, followed by a rapid decrease after birth. A positive correlation between cell-free fetal DNA concentrations and the number of GFP-positive pups was also observed. The increase in cell-free fetal DNA concentrations prior to labor at term was not linked to a surge in any specific cytokine/chemokine; yet, specific chemokines (i.e., CCL2, CCL7, and CXCL2) increased as gestation progressed and maintained elevated levels in the postpartum period. In addition, cell-free fetal DNA concentrations increased prior to systemic inflammation-induced preterm birth, which was associated with a strong cytokine response in the maternal circulation. However, cell-free fetal DNA concentrations were not increased prior to intra-amniotic inflammation-induced preterm birth, but in this model, a mild inflammatory response was observed in the maternal circulation. Collectively, these findings suggest that an elevation in cell-free fetal DNA concentrations in the maternal circulation precedes the physiological process of labor at term and the pathological process of preterm labor linked with systemic inflammation, but not that associated with intra-amniotic inflammation.

The Cellular Transcriptome in the Maternal Circulation During Normal Pregnancy: A Longitudinal Study

Pregnancy represents a unique immunological state in which the mother adapts to tolerate the semi-allogenic conceptus; yet, the cellular dynamics in the maternal circulation are poorly understood. Using exon-level expression profiling of up to six longitudinal whole blood samples from 49 pregnant women, we undertook a systems biology analysis of the cellular transcriptome dynamics and its correlation with the plasma proteome. We found that: (1) chromosome 14 was the most enriched in transcripts differentially expressed throughout normal pregnancy; (2) the strongest expression changes followed three distinct longitudinal patterns, with genes related to host immune response (e.g., MMP8, DEFA1B, DEFA4, and LTF) showing a steady increase in expression from 10 to 40 weeks of gestation; (3) multiple biological processes and pathways related to immunity and inflammation were modulated during gestation; (4) genes changing with gestation were among those specific to T cells, B cells, CD71+ erythroid cells, natural killer cells, and endothelial cells, as defined based on the GNF Gene Expression Atlas; (5) the average expression of mRNA signatures of T cells, B cells, and erythroid cells followed unique patterns during gestation; (6) the correlation between mRNA and protein abundance was higher for mRNAs that were differentially expressed throughout gestation than for those that were not, and significant mRNA-protein correlations were observed for genes part of the T-cell signature. In summary, unique changes in immune-related genes were discovered by longitudinally assessing the cellular transcriptome in the maternal circulation throughout normal pregnancy, and positive correlations were noted between the cellular transcriptome and plasma proteome for specific genes/proteins. These findings provide insights into the immunobiology of normal pregnancy.

Usefulness and reliability of cell free fetal DNA screening for main trisomies in case of atypical profile on first trimester maternal serum screening

Background

Patients with atypical values of HCG and/or PAPP-A are at higher risk of chromosomal abnormality and vascular complications of pregnancy. The performance of cfDNA in this particular population has not yet been evaluated.

Objectives

The primary objective was to evaluate the usefulness and reliability of cfDNA in screening for trisomy 21, 18 and 13 for patients with HCG < 0.25 multiple of median (MoM), HCG > 5.0 MoM and/or PAPP-A < 0.25 MoM, PAPP-A > 2.5 MoM. The secondary objective was to evaluate the contribution of cfDNA assay for the prediction of pregnancy’s vascular complications.

Method

Between June 2016 and July 2017, we analysed a women cohort from all over France who had at least one first trimester serum biomarker outside of normal range, in a retrospective, observational and multicentre study. Patients were included if they had a single pregnancy, normal first trimester ultrasound examination, whatever the result of the combined first trimester screening test was. The cfDNA was analysed by massive parallel sequencing technique. The accuracy of cfDNA assay was evaluated by calculation of sensitivity and specificity, and multivariate regression analysis was used to search for predictive factors for pregnancy’s vascular complications.

Results

Among the 498 patients who underwent a cfDNA assay in this context, twenty-one (4.2%) were excluded because of loss to follow-up. Out of 477, test failure occurred for four patients initially, reduced to two patients (0.4%) after redrawn. CfDNA was positive for Trisomy 21 (n = 19), Trisomy 18 (n = 6) and Trisomy 13 (n = 1) and negative in 449. The sensitivity of cfDNA assay for trisomy 21 screening was 100% (19/19) (IC 95% 82.4–100) and specificity 100% (458/458) (IC 95% 99.2–100). Among the 447 patients included for prediction of vascular complications, there were four cases of pregnancy induced hypertension and 10 cases of preeclampsia, for which no predictive factor was identified. Intra Uterine growth restriction under 5th percentile (n = 44, 9.8%) was significantly associated with a low fetal fraction (OR = 0.87, IC 95% 0.79–0.96, p = 0.006).

Conclusion

cfDNA assay is an effective and reliable tool for women with atypical profile of first trimester serum biomarkers.

Development of the human placenta

The placenta is essential for normal in utero development in mammals. In humans, defective placental formation underpins common pregnancy disorders such as pre-eclampsia and fetal growth restriction. The great variation in placental types across mammals means that animal models have been of limited use in understanding human placental development. However, new tools for studying human placental development, including 3D organoids, stem cell culture systems and single cell RNA sequencing, have brought new insights into this field. Here, we review the morphological, molecular and functional aspects of human placental formation, with a focus on the defining cell of the placenta - the trophoblast.

Could high levels of cell-free DNA in maternal blood be associated with maternal health and perinatal outcomes?

The aim of this study was to evaluate the maternal and foetal factors affect higher cell-free DNA (cfDNA) levels and to investigate a possible relationship between high cfDNA levels and adverse perinatal outcomes. From a total of 4594 women who underwent non-invasive prenatal testing from January 2016 to March 2018 in our hospital, 112 women had high levels of cfDNA, which was not appropriate for testing. Maternal characteristics and perinatal outcomes were compared between patients with high levels of cfDNA and normal levels of cfDNA. Patients with high levels of cfDNA had greater risks than patients with normal cfDNA levels of pregnancy complications but no statistically significant difference was found. Patients with high cfDNA levels had higher foetal death rates with a statistically significant difference (9.8% versus 1.8%, p = .024). An increase in foetal death could be expected in patients with increased cfDNA levels; therefore, these patients should be carefully followed up during pregnancy.IMPACT STATEMENTWhat's already known about this topic? Most studies about cfDNA levels are focussed on the foetal fraction. There are new arguments about maternal health and cfDNA. It is known that autoimmune diseases as systemic lupus erythematosus (SLE) and maternal obesity increase cell turnover. There are also clinical studies suggesting a relationship between low molecular weight heparin therapy and the amount of cfDNA.What do the results of this study add? This is the first study evaluating the maternal and foetal biological factors affecting cfDNA concentrations and investigating the possible relationship between high cfDNA levels and adverse perinatal outcomes in patients with high levels of cfDNA compared to patients with normal levels of cfDNA. In the present study, it was found that an increase in foetal death could be expected in patients with higher cfDNA levels.What are the implications of these findings for clinical practice and/or further research? If potential effects and underlying causes of increased cfDNA could be explained, cfDNA might be used as a biomarker for adverse perinatal outcomes.

Novel Epigenetic Biomarkers in Pregnancy-Related Disorders and Cancers

As the majority of cancers and gestational diseases are prognostically stage- and grade-dependent, the ultimate goal of ongoing studies in precision medicine is to provide early and timely diagnosis of such disorders. These studies have enabled the development of various new diagnostic biomarkers, such as free circulating nucleic acids, and detection of their epigenetic changes. Recently, extracellular vesicles including exosomes, microvesicles, oncosomes, and apoptotic bodies have been recognized as powerful diagnostic tools. Extracellular vesicles carry specific proteins, lipids, DNAs, mRNAs, and miRNAs of the cells that produced them, thus reflecting the function of these cells. It is believed that exosomes, in particular, may be the optimal biomarkers of pathological pregnancies and cancers, especially those that are frequently diagnosed at an advanced stage, such as ovarian cancer. In the present review, we survey and critically appraise novel epigenetic biomarkers related to free circulating nucleic acids and extracellular vesicles, focusing especially on their status in trophoblasts (pregnancy) and neoplastic cells (cancers).

The association of HBB-related significant hemoglobinopathies and low fetal fraction on noninvasive prenatal screening for fetal aneuploidy

Objectives: HBB-related significant hemoglobinopathies have been anecdotally associated with low fetal fraction on noninvasive prenatal screening (NIPS). We sought to compare the difference in fetal fraction using NIPS in women with HBB-related significant hemoglobinopathies (HSH) and women with normal hemoglobin.Study design: This is a retrospective case-control study. Cases were women with a diagnosis of HSH using NIPS from a commercial laboratory. The comparison group was women with hemoglobin AA from a tertiary care center database. We tested for differences in median fetal fraction using quantile regression analysis, adjusting for maternal body weight and gestational age.Results: This study includes 35 women with clinically significant HSH and a comparison group of 636 women with hemoglobin AA. Adjusting for gestational age and body weight, the median fetal fraction was 4.1 point lower in the HSH than in the comparison group (β - 4.1; 95% -5.7 to -2.5, p < .05). The rate of no-calls due to low fetal fraction was significantly higher in the clinically significant HSH group than in the comparison group [HSH: n = 9/35, 25.7% versus comparison: n = 32/636, 5.0% (p < .001)].Conclusion: Women with HSH were more likely to have a lower fetal fraction and ultimately a five-fold higher no-call rate. What's already known about this topic?Low fetal fraction is one of the most common causes of no-call result in noninvasive prenatal screeningHigh maternal weight, early gestational age and fetal aneuploidies are associated with low fetal fraction What does this study add?HBB-related significant hemoglobinopathies are associated with low fetal fractionReduction in fetal fraction due to HBB-related significant hemoglobinopathies may also result in higher no-call rate.

Association between fetal fraction at the second trimester and subsequent spontaneous preterm birth

OBJECTIVE

To evaluate the association between the fetal fraction of cell-free DNA at the second trimester and subsequent spontaneous preterm birth.

METHODS

In this retrospective cohort study, data were collected from women with singleton pregnancies who underwent noninvasive prenatal testing at 14 to 25 weeks of gestation. The eligible patients were classified into three groups according to pregnancy outcome: birth at ≥37 weeks of gestation (term group), delivery at <34 weeks of gestation (early spontaneous preterm), and delivery at 34⁺⁰ to 36⁺⁶  weeks of gestation (late spontaneous preterm). Stepwise linear regression was performed to determine the maternal characteristics associated with the fetal fraction of cell-free DNA. Logistic regression was used to determine the relationship between the fetal fraction of cell-free DNA and pregnancy outcomes by adjusting for history of preterm birth.

RESULTS

A total of 8129 singleton pregnancies met the recruitment criteria. Among them, 7790 (95.83%) were in the term group, 284 (3.49%) were in the late spontaneous preterm group, and 55 (0.68%) were in the early spontaneous preterm group. The fetal fraction of cell-free DNA was negatively correlated with body mass index, maternal age, nulliparity, and history of spontaneous preterm birth; positively correlated with gestational age; and not correlated with assisted reproduction or surface antigen of hepatitis B virus (HBsAg) positivity. After adjusting for history of preterm birth, a logistic regression analysis demonstrated no statistically significant associations between the fetal fraction of cell-free DNA and spontaneous preterm birth in any of the preterm groups (<34 weeks, 34⁺⁰ to 36⁺⁶  weeks, and <37 weeks).

CONCLUSION

Our preliminary study found no relationship between the fetal fraction on NIPT at the second trimester and subsequent spontaneous preterm birth.

[Cell-free DNA fraction: Can it be used to evaluate the risk of obstetrical issues?]

OBJECTIVE

The aim of the study was to evaluate if fetal cell-free DNA (cfDNA) fraction circulating in maternal blood at the beginning of the second trimester is associated with obstetrical complications.

METHODS

This is a retrospective unicentric study conducted at the hospital of Poissy Saint Germain between the 1^st January 2015, and the 31^st. December 2016, Each woman who had a genetic counseling in order to realize a non-invasive prenatal test (NIPT) was included. Only singleton pregnancies with a documented-issue were analysed. The primary criteria was a composite criteria, defined as the occurrence of preeclampsia, in utero fetal growth, or a spontaneous preterm delivery. A descriptive analyse was first conducted, secondly completed by a sub-group one: "high fetal fraction" (>90^th percentile) group, "low fetal-fraction" group (<10^th percentile) and "medium fetal-fraction" (control group) group.

RESULTS

A total of 417 women had a cfDNA test, which was performed at a mean gestational age of 17.1 weeks of gestation. A total of 17% of pregnancies met the primary criteria. Among them, there were 8 (1.9%) pre-eclampsia, 49 (11.8%) intra-uterine growth restriction and 14 (3.4%) preterm births. There was no significant difference for the occurrence of the primary criteria (P>0.99) and of each obstetrical complication between each group.

CONCLUSION

Fetal cf-DNA fraction measured at the beginning of the second trimester is not associated with common obstetrical complications.

Influence of Body Mass Index on Fetal Fraction Increase With Gestation and Cell-Free DNA Test Failure

OBJECTIVE

To assess the influence of body mass index (BMI) on fetal fraction increase with gestational age and on the rates of test failure.

METHODS

We performed a cross-sectional study of consecutive singleton pregnancies in which cell-free DNA screening for fetal aneuploidies was performed from 10 weeks of gestation, between May 2013 and January 2018, at two fetal medicine clinics in Australia using one of two different platforms. Maternal characteristics, fetal fraction, and failure after a first attempt ("no-call") and after resampling ("test failure") were recorded. Body mass index was classified as normal (BMI less than 25.0), overweight (BMI 25.0-29.9), obesity class I (BMI 30.0-34.9), and obesity classes II and III (BMI 35.0 or greater). Fetal fraction and proportions of no-call results and test failure were compared between the groups.

RESULTS

Of 14,223 singleton pregnancies included, 8,583 (60.3%) were screened with platform A and 5,640 (39.7%) with platform B. Median fetal fraction values were lower, and no-call and failure rates were higher in increased BMI groups across both platforms (P<.001 in both). When compared with women with normal BMIs, women with BMIs of 35 or greater had a significantly smaller increase in fetal fraction (0.1 vs 0.3 units/wk, P<.001, in both platforms). In this subgroup, when compared with women with normal BMIs, the odds ratios for a no-call result were 22.0 (95% CI 13.8-35.3, 16.6% vs 0.9%) and 8.0 (95% CI 4.1-15.6, 7.8% vs 1.0%) and for a failed test were 25.0 (95% CI 11.2-55.7, 6.4% vs 0.3%) and 5.8 (95% CI 2.0-17.3, 2.7% vs 0.5%) using platforms A and B, respectively.

CONCLUSION

The increase in fetal fraction throughout gestation in women with BMIs of 35 or above is minimal. Postponing the test is unlikely to reduce test failure rates in this population.

Non-invasive Prenatal Testing Using Fetal DNA

Non-invasive prenatal diagnosis (NIPD) is based on fetal DNA analysis starting from a simple peripheral blood sample, thus avoiding risks associated with conventional invasive techniques. During pregnancy, the fetal DNA increases to approximately 3-13% of the total circulating free DNA in maternal plasma. The very low amount of circulating cell-free fetal DNA (ccffDNA) in maternal plasma is a crucial issue, and requires specific and optimized techniques for ccffDNA purification from maternal plasma. In addition, highly sensitive detection approaches are required. In recent years, advanced ccffDNA investigation approaches have allowed the application of non-invasive prenatal testing (NIPT) to determine fetal sex, fetal rhesus D (RhD) genotyping, aneuploidies, micro-deletions and the detection of paternally inherited monogenic disorders. Finally, complex and innovative technologies such as digital polymerase chain reaction (dPCR) and next-generation sequencing (NGS) (exhibiting higher sensitivity and/or the capability to read the entire fetal genome from maternal plasma DNA) are expected to allow the detection, in the near future, of maternally inherited mutations that cause genetic diseases. The aim of this review is to introduce the principal ccffDNA characteristics and their applications as the basis of current and novel NIPT.

Low fetal fraction of cell-free DNA predicts placental dysfunction and hypertensive disease in pregnancy

OBJECTIVE

To examine the association of low fetal fraction of cell-free DNA (cfDNA) with placental compromise and adverse perinatal outcomes.

MATERIALS AND METHODS

This was a retrospective cohort utilizing a sample of convenience including 639 women undergoing cfDNA screening at our institution from January 2013 to January 2017. Low fetal fraction was defined as less than the 25th percentile. Indicators of placental compromise were examined individually and as a composite outcome, including hypertensive disease of pregnancy, intrauterine growth restriction, abruption, and oligohydramnios. Neonatal outcomes, including preterm delivery, low Apgar scores, and small for gestational age, also were examined. We calculated risk ratios (RR) and 95% confidence intervals (CI).

RESULTS

Low fetal fraction was associated with placental compromise (RR 1.6 [CI 1.1-2.2]), hypertensive disease of pregnancy (RR 1.6 [CI 1.003-2.6]), and preeclampsia with severe features (RR 3.3 [CI 1.2-8.9]). Low fetal faction was not associated with preterm delivery, low Apgar scores, or small for gestational age.

CONCLUSIONS

Low fetal fraction of cfDNA among asymptomatic women may serve as a predictor of subsequent placental dysfunction and hypertensive disease.

Cell-Free DNA (cfDNA) Fetal Fraction in Early- and Late-Onset Fetal Growth Restriction

OBJECTIVE

Our objective was to retrospectively evaluate whether the levels of cell-free DNA (cfDNA) fetal fraction differed in the first trimester of pregnancies between controls and those who subsequently developed early- or late-onset fetal growth restriction (FGR).

METHODS

This was a case-control study conducted between May 2015 and May 2018 in 231 low-risk women who had received first trimester screening for major fetal aneuploidies (Panorama, Natera, San Carlos, CA, USA). Early- and late-onset FGR developed in 5 and 16 women, respectively, according to Delphi criteria. Multiples of median (MoM) were used to evaluate the differences in cfDNA fetal fraction between cases and controls. cfDNA fetal fraction was adjusted for gestational age (from 10 + 0 to 13 + 6 gestational weeks) and maternal weight (43-96 kg).

RESULTS

The median cfDNA fetal fractions for controls and early- and late-onset FGR were 1.00 (interquartile range [IQR] 0.89-1.12), 0.69 (IQR 0.44-0.84) and 0.93 (IQR 0.83-1.03) MoM, respectively. Statistically lower cfDNA fetal fraction MoM values were observed only in patients with early-onset FGR (Kruskal-Wallis test with Dunn post hoc test). In a 1:35 ratio (one case of early-onset FGR: 35 controls), the mean observed rank of 2.00 ± 2.23 in the cases was significantly lower than the expected 18.97 ± 10.17 (p < 0.001).

CONCLUSIONS

Low-risk pregnancies that developed early-onset FGR had lower cfDNA fetal fractions than did the matched controls. This result is consistent with the placental dysfunction typical of early-onset FGR. For possible clinical use, the cfDNA fetal fraction would yield a better predictive value if adjusted for maternal weight, since maternal weight affects both cfDNA fetal fraction and the occurrence of FGR.