Screening for trisomies by cfDNA testing of maternal blood in twin pregnancy: update of The Fetal Medicine Foundation results and meta-analysis

Cell-free DNA screening in twin pregnancies: A more accurate and reliable screening tool

OBJECTIVE

Outcome data from cell-free DNA (cfDNA) screening in twin gestations are limited. This study adds an appreciable number of confirmed outcomes to the literature, and assesses performance of cfDNA screening in twins over a 4.5-year period at one large clinical laboratory.

METHOD

Prenatal cytogenetic and SNP microarray results were cross-referenced with cfDNA results for twin pregnancies, yielding 422 matched cases. Using diagnostic results as truth, performance of cfDNA screening in this population was assessed.

RESULTS

Of the 422 twin pregnancies with both cfDNA and diagnostic results, 3 specimens failed amniocyte analysis, and 48 samples (11.5%) were nonreportable from the initial cfDNA draw. Analysis of the 371 reportable samples demonstrated a collective sensitivity of 98.7% and specificity of 93.2% for trisomies 21/18/13. Positive predictive values (PPVs) in this study population, which is enriched for aneuploidy, were 78.7%, 84.6%, and 66.7% for trisomy 21, 18, and 13, respectively.

CONCLUSION

CfDNA screening in a cohort of twin pregnancies with matched diagnostic results showed superior performance compared to traditional serum biochemical screening in twins. This study adds to a growing body of evidence suggesting that cfDNA is an accurate and reliable screening tool for the major trisomies in twin pregnancies.

Applying high-throughput sequencing to identify and evaluate foetal chromosomal deletion and duplication

The present study aimed to estimate the clinical performance of non-invasive prenatal testing (NIPT) based on high-throughput sequencing method for the detection of foetal chromosomal deletions and duplications. A total of 6348 pregnant women receiving NIPT using high-throughput sequencing method were included in our study. They all conceived naturally, without twins, triplets or multiple births. Individuals showing abnormalities in NIPT received invasive ultrasound-guided amniocentesis for chromosomal karyotype and microarray analysis at 18-24 weeks of pregnancy. Detection results of foetal chromosomal deletions and duplications were compared between high-throughput sequencing method and chromosomal karyotype and microarray analysis. Thirty-eight individuals were identified to show 51 chromosomal deletions/duplications via high-throughput sequencing method. In subsequent chromosomal karyotype and microarray analysis, 34 subchromosomal deletions/duplications were identified in 26 pregnant women. The observed deletions and duplications ranged from 1.05 to 17.98 Mb. Detection accuracy for these deletions and duplications was 66.7%. Twenty-one deletions and duplications were found to be correlated with the known abnormalities. NIPT based on high-throughput sequencing technique is able to identify foetal chromosomal deletions and duplications, but its sensitivity and specificity were not explored. Further progress should be made to reduce false-positive results.

Update on noninvasive prenatal testing: A review based on current worldwide research

Eight years have passed since noninvasive prenatal testing (NIPT) was clinically evaluated and data on NIPT for trisomy 21, 18 and 13 were collected. The data revealed that NIPT is more accurate than conventional first-trimester screening. However, there is still insufficient data regarding the clinical use of NIPT results in detecting sex chromosome aneuploidies or whole-genome regions. NIPT is already being used as a clinical screening method globally. However, it is an unconfirmed diagnostic test and the results must be interpreted with caution as they may yield false negatives, false positives or inconclusive results. Therefore, the aim of this review is to highlight the current status of information, including the different methodologies, shortcomings and implications, regarding NIPT after its adoption worldwide. It is important to include genetic counseling when implementing NIPT. Going forward, the knowledge obtained to date, including the associated shortcomings, must be considered in evaluating the effectiveness of NIPT in detecting genetic abnormalities.

Monochorionic diamniotic twins: What do I tell the prospective parents?

Monochorionic diamniotic twins occur in about 1 in 300 pregnancies. Compared with dichorionic twins, they face increased risks because of the shared circulation. In about 15%, an imbalance in blood exchange occurs, such as twin-twin transfusion syndrome and twin anemia polycythemia sequence. In this review, we summarize the latest evidence on the management of monochorionic diamniotic twin pregnancies and their specific complications, with a focus on information that is relevant for prospective parents.

Clinical performance of non-invasive prenatal testing for trisomies 21, 18 and 13 in twin pregnancies: A cohort study and a systematic meta-analysis

INTRODUCTION

The objective of this study was to report on the clinical performance of non-invasive prenatal testing (NIPT) for trisomies 21, 18 and 13 in twin pregnancies and to define the performance of NIPT by combining our cohort study results with published studies in a systematic meta-analysis.

MATERIAL AND METHODS

A cohort study was carried out in the First Affiliated Hospital of Sun Yat-sen University and Kanghua Hospital. Meanwhile, searches of PubMed, EMBASE, The Cochrane Library and Web of Science for all relevant peer-reviewed articles were performed with a restriction to English language publication before 15 June 2019. Quality assessments were conducted with the Quality Assessment Tool for Diagnostic Accuracy Studies-2 checklist. Data analysis, heterogeneity, subgroup analysis and publication bias were carried out using META-DISC 1.4 and STATA 12.0.

RESULTS

In all, 141 twin pregnancies included in our cohort study; confirmation revealed one true-positive case for trisomy 21 and 140 true-negative cases. The sensitivity and specificity for trisomy 21 by NIPT were both 100%. Twenty-two eligible studies were enrolled in this meta-analysis together with our study. There were 199 cases of trisomy 21, 58 cases of trisomy 18, 14 cases of trisomy 13 and 6347 cases of euploids in total. For trisomy 21, NIPT showed the pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio and diagnostic odds ratio were 0.99, 1.00, 145.81, 0.06 and 1714.09, respectively. For trisomy 18, the pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio and diagnostic odds ratio were 0.88, 1.00, 200.98, 0.19 and 483.68, respectively.

CONCLUSIONS

The performance of NIPT for trisomy 21 in twin pregnancy was excellent and it was similar to that reported in singleton pregnancy. However, due to publication bias (trisomy 18) and small number of cases (trisomy 13), accurate assessment of the predictive performance of NIPT for trisomies 18 and 13 could not be achieved.

Assessing the practice of LuPOR for poor responders: a prospective study evaluating follicular fluid cfDNA levels during natural IVF cycles

PURPOSE

The aim of this study is to provide data on the practice of Luteal Phase Oocyte Retrieval (LuPOR). The authors assess cell-free DNA levels in follicular fluid (ff cfDNA) from poor responders undergoing natural cycles, and comparing it to respective data originating from follicular phase oocyte retrievals.

METHODS

Forty-seven women were eligible for this prospective study. Participants were classified as poor responders based on Bologna criteria while being detected with a second follicular wave. Follicular fluid was collected and prepared for cfDNA extraction. Levels of cfDNA were quantified via Q-PCR employing the ALU115 and ALU247 primers. These primers are associated with apoptotic and necrotic events. Levels of ff cfDNA resulting from follicular phase oocyte retrieval (FoPOR) and LuPOR-performed in a single menstrual cycle were associated with the number and maturation status of yielded oocytes and the number and fertilization status of resulting zygotes. Survival rate following thawing of cryopreserved zygotes, along with the resulting number of cleavage stage and blastocyst stage embryos are provided.

RESULTS

Mean levels of ALU115 were significantly lower during FoPOR when compared to LuPOR (0.79 ± 0.72 vs 1.46 ± 1.59 ng/μl, p = 0.02). Regarding the FoPOR group, a significant positive correlation of serum estradiol and ALU115 concentration (p = 0.04) was revealed. A significant negative correlation between serum estradiol and cfDNA integrity was observed both during FoPOR (p = 0.03) and LuPOR (p = 0.03). A significant lower number of retrieved (1.09 ± 0.28 vs 1.29 ± 0.58, p = 0.02) and MII oocytes (0.77 ± 0.55 vs 1.08 ± 0.61, p = 0.02) was observed when comparing the FoPOR to LuPOR groups respectively. The integrity of cfDNA was observed to be higher in FoPOR originating embryos that arrested either prior to cleavage (0.28 ± 0.13 vs 0.17 ± 0.10, p = 0.006) or prior to blastocyst formation (0.28 ± 0.12 vs 0.13 ± 0.06, p = 0.04). In the case of LuPOR originating embryos, cfDNA integrity was observed to be higher in embryos that arrested only prior to the blastocyst stage (0.27 ± 0.20 vs 0.11 ± 0.07, p = 0.008). Similarly, cfDNA integrity was observed to be lower in top quality blastocysts originating from FoPOR (0.07 ± 0.04 vs 0.17 ± 0.05, p = 0.03) and in top quality cleavage stage embryos (0.09 ± 0.06 vs 0.31 ± 0.22, p = 0.01) and blastocysts (0.06 ± 0.02 vs 0.14 ± 0.06, p = 0.02) originating from LuPOR.

CONCLUSIONS

Our results indicate that ff originating from LuPOR presents with higher levels of cfDNA. The higher cfDNA levels are attributed to mainly apoptotic events, as the ALU247 levels and DNA integrity did not differ statistically significantly between FoPOR and LuPOR. The absolute mean level of ALU247 corresponding to necrotic events was higher in LuPOR. Regarding embryological data, cfDNA integrity was correlated with both number and quality of cleavage stage embryos in both FoPOR and LuPOR, along with blastocyst stage embryos in LuPOR. Necrotic events were associated with poorer blastocyst formation rate and blastocyst quality in LuPOR. As the comparison between FoPOR and LuPOR results to similar IVF laboratory data, the practice of LuPOR may stand as a promising approach for poor responders, while it merits further investigation.

Increased nuchal translucency at 11-13 weeks' gestation and outcome in twin pregnancy

OBJECTIVE

To investigate the value of increased fetal nuchal translucency thickness (NT) at the 11-13-week scan in the prediction of adverse outcome in dichorionic (DC), monochorionic diamniotic (MCDA) and monochorionic monoamniotic (MCMA) twin pregnancies.

METHODS

This was a retrospective analysis of prospectively collected data on twin pregnancies undergoing routine ultrasound examination at 11-13 weeks' gestation between 2002 and 2019. In pregnancies with no major defects or chromosomal abnormalities, we examined the value of increased NT ≥ 95^th percentile in one or both fetuses in the prediction of, first, miscarriage or death of one or both fetuses at < 20 and < 24 weeks' gestation in DC, MCDA and MCMA twin pregnancies, second, death of one or both fetuses or neonates at ≥ 24 weeks in DC, MCDA and MCMA twin pregnancies, third, development of twin-twin transfusion syndrome (TTTS) or selective fetal growth restriction (sFGR) treated by endoscopic laser surgery at < 20 and ≥ 20 weeks' gestation in MCDA pregnancies, and, fourth, either fetal loss or laser surgery at < 20 weeks' gestation in MCDA pregnancies.

RESULTS

The study population of 6225 twin pregnancies included 4896 (78.7%) DC, 1274 (20.5%) MCDA and 55 (0.9%) MCMA pregnancies. The incidence of NT ≥ 95^th percentile in one or both fetuses in DC twin pregnancies was 8.3%; in MCDA twins the incidence was significantly higher (10.4%; P = 0.016), but in MCMA twins it was not significantly different (9.1%; P = 0.804) from that in DC twins. In DC twin pregnancies, the incidence of high NT was not significantly different between those with two survivors and those with adverse outcome. In MCMA twin pregnancies, the number of cases was too small for meaningful assessment of the relationship between high NT and adverse outcome. In MCDA twin pregnancies with at least one fetal death or need for endoscopic laser surgery at < 20 weeks' gestation, the incidence of NT ≥ 95^th percentile was significantly higher than in those with two survivors (23.5% vs 9.8%; P < 0.0001). Kaplan-Meier analysis in MCDA twin pregnancies showed that, in those with NT ≥ 95^th percentile, there was significantly lower survival at < 20 weeks' gestation than in those with NT < 95^th percentile (P = 0.001); this was not the case for survival at ≥ 20 weeks (P = 0.960). The performance of screening by fetal NT ≥ 95^th percentile for prediction of either fetal loss or need for endoscopic laser surgery at < 20 weeks' gestation was poor, with a detection rate of 23.5% at a false-positive rate of 8.9%, and the relative risk, in comparison to fetal NT < 95^th percentile, was 2.640 (95% CI, 1.854-3.758; P < 0.0001). In MCDA twin pregnancies, the overall rate of fetal loss or need for laser surgery at < 20 weeks' gestation was 10.7% but, in the subgroups with NT ≥ 95^th and NT ≥ 99^th percentiles, which constituted 10.4% and 3.3% of the total, the rates increased to 24.1% and 40.5%, respectively.

CONCLUSIONS

In MCDA twin pregnancies with no major fetal abnormalities, measurement of NT at the 11-13-week scan is a poor screening test for adverse pregnancy outcome. However, the finding in one or both fetuses of NT ≥ 95^th percentile, and more so ≥ 99^th percentile, is associated with a substantially increased risk of fetal loss or need for endoscopic laser surgery at < 20 weeks' gestation. The extent to which closer monitoring and earlier intervention in the high-risk group can reduce these complications remains to be determined. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

First-trimester screening for trisomies in pregnancies with vanishing twin

OBJECTIVES

To examine multiples of the median (MoM) values of serum free beta-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A) in a large series of pregnancies with a vanishing twin, determine the association of these values with the interval between embryonic death and blood sampling, and develop a model that would allow incorporation of these metabolites in first-trimester combined screening for trisomy.

METHODS

This was a retrospective study comparing maternal serum free β-hCG and PAPP-A levels at 11-13 weeks' gestation in 528 dichorionic pregnancies with a vanishing twin, including 194 (36.7%) with an empty gestational sac and 334 (63.3%) with a dead embryo, with those in 5280 normal singleton pregnancies matched for method of conception and date of examination. In vanishing-twin pregnancies with a dead embryo, marker levels were examined in relation to the estimated time between embryonic death and maternal blood sampling.

RESULTS

First, in pregnancies with a vanishing twin, median free β-hCG MoM was not significantly different from that in normal singleton pregnancies (1.000; 95% CI, 0.985-1.016 vs 0.995; 95% CI, 0.948-1.044; P = 0.849). Second, PAPP-A MoM was higher in vanishing-twin pregnancies than in normal singleton pregnancies (1.000; 95% CI, 0.985-1.015), both in the group with an empty gestational sac (1.165; 95% CI, 1.080-1.256; P = 0.0001) and in that with a dead embryo (1.175; 95% CI, 1.105-1.249; P < 0.0001). Third, in vanishing-twin pregnancies with a dead embryo, PAPP-A MoM was related inversely to the interval between estimated gestational age at embryonic demise and blood sampling (P < 0.0001). Fourth, in first-trimester screening for trisomy 21 in singleton pregnancies, the estimated detection rate, at a 5% false-positive rate, was 82% in screening by a combination of maternal age and fetal nuchal translucency thickness, and this increased to 86% with the addition of serum free β-hCG and to 91% with the addition of serum PAPP-A. Fifth, similar performance of screening can be achieved in pregnancies with a vanishing twin, provided the appropriate adjustments are made to the level of PAPP-A for the interval between estimated gestational age at embryonic demise and blood sampling.

CONCLUSIONS

First-trimester screening for trisomy in pregnancies with a vanishing twin should rely on a combination of maternal age, fetal nuchal translucency thickness and serum free β-hCG, as in singleton pregnancy, without the use of serum PAPP-A. Alternatively, PAPP-A can be included but only after appropriate adjustment for the interval between estimated gestational age at fetal demise and blood sampling. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Non-invasive prenatal test to screen common trisomies in twin pregnancies

Objectives

Recent years have witnessed a shift from invasive methods of prenatal screening to non-invasive strategies. Accordingly, non-invasive prenatal testing (NIPT) using cell-free fetal DNA in maternal plasma has gained a considerable deal of interest from both geneticists and obstetricians. Efficacy of this method in identification of common aneuploidies has been extensively assessed in singleton pregnancies. However, a limited number of studies have addressed the twin pregnancies. In this context, the present study is aimed at identification of the efficacy of NIPT in twin pregnancies.

Methods

NIPT was performed on twin pregnancies to screen trisomies 13, 18 and 21. Pregnant women referring to Nilou Clinical Laboratory between March 2016 and December 2018 were included in this research.

Results

In the current study, a total 356 twin pregnancies were screened in search for trisomies 13, 18 and 21. 6 cases exhibited positive NIPT results in which the presence of trisomies 13, 18 and 21 was confirmed by fetal karyotype in 1, 2 and 2 cases, respectively. One twin pregnancy showed normal karyotype. The combined false-positive rate for these trisomies was 0.28%. No false negative case was observed. The combined sensitivity and specificity of NIPT in twin pregnancies were 100 and 99.7%, respectively.

Conclusion

The results of the current study verify the feasibility, sensitivity and specificity of NIPT in twin pregnancies.

Non-Invasive Prenatal Testing beyond Trisomies

The last decade has seen incredible advances in the genetic era, in next-generation sequencing of cell-free DNA in the maternal plasma, detecting abnormal fetal chromosomes. Non-invasive prenatal testing (NIPT) has showed increased sensitivity and specificity for Down syndrome superior to any other screening test. Technical advances have made possible the detection of other conditions which does not necessarily mean clinical benefit for the patient. Private laboratories have added multiple conditions in the panel of NIPT, but some of these abnormalities are so rare, that their prevalence is not even clear. Data regarding clinical performance of extended NIPT is lacking. Implementation of such a test has to be carefully weighed, and not only the benefits but also the harm should be taken into account.

Implementation of maternal blood cell-free DNA testing in early screening for aneuploidies

Several externally blinded validation and implementation studies in the last 9 years have shown that it is now possible, through analysis of cell-free (cf) DNA in maternal blood, to effectively detect a high proportion of fetuses affected by trisomies 21, 18, and 13 at a much lower false-positive rate (FPR) than all other existing screening methods. This article is aimed at reviewing technical and clinical considerations for implementing cfDNA testing in routine practice, including methods of analysis, performance of the test, models for clinical implementation, and interpretation of results.

Validation of fetal DNA fraction estimation and its application in noninvasive prenatal testing for aneuploidy detection in multiple pregnancies

OBJECTIVE

To analyze the fetal fraction, fetal sex, and chromosomal aneuploidy in multiple pregnancies using noninvasive prenatal testing (NIPT).

METHOD

A total of 362 pregnant women including 203 singleton pregnancies, 69 twins, and 90 higher-order multiple pregnancies were recruited. Fetal fractions estimated by size ratio-based and Y chromosome-based approaches in singleton pregnancies with male fetus were used as source data to establish the model. The model was then applied to multiple pregnancies for fetal fraction estimation. By comparing the fetal fractions estimated by size ratio to those estimated by Y chromosome or autosomal chromosomes, fetal sex and chromosomal aneuploidy can be analyzed.

RESULTS

The size ratio-based approach has been well established in estimating fetal fractions for twin and higher-order multiple pregnancies. Fetal fraction had a positive correlation with gestational age in twin and triplet pregnancies. Fetal sex was determined with accuracies of 98.6% (95% CI, 92.19%-99.96%) in twins and 97.6% (95% CI, 91.76%-99.71%) in triplet pregnancies. Four trisomy 21, one trisomy 18, and one trisomy 13 cases were detected by NIPT. Two trisomy 21 singleton pregnancies and one trisomy 21 twin pregnancy were confirmed by karyotyping.

CONCLUSION

Fetal sex and chromosomal aneuploidy in multiple pregnancies can be determined using NIPT.

Current landscape of prenatal genetic screening and testing

Pregnant patients should be offered the option of prenatal genetic screening and diagnostic testing. The type of screening and testing offered to a patient may depend on various factors including but not limited to age, family history, fetal findings, exposures, and patient preferences. Prenatal screening is available for a variety of genetic conditions including aneuploidy, congenital abnormalities, and carrier status. Diagnostic testing options include karyotype, prenatal microarray, as well as next-generation sequencing. The various options differ in methodology, accuracy, timing and indication for testing, and information they provide. Given that the technologies related to prenatal testing are rapidly evolving and improving, the array of available screening and testing modalities are increasing. This article reviews the current offerings in prenatal screening and diagnosis.

First-trimester screening for trisomies by cfDNA testing of maternal blood in singleton and twin pregnancies: factors affecting test failure

OBJECTIVE

To examine factors affecting the rate of failure to obtain a result from cell-free DNA (cfDNA) testing of maternal blood for fetal trisomies 21, 18 and 13 in singleton and twin pregnancies in the first trimester.

METHODS

This was a prospective study of 23 495 singleton and 928 twin pregnancies undergoing screening for fetal trisomy by targeted cfDNA testing at 10 + 0 to 14 + 1 weeks' gestation. Multivariate logistic regression analysis was used to determine significant predictors of failure to obtain a result after first sampling.

RESULTS

There was no result from cfDNA testing after first sampling in 3.4% (798/23 495) of singletons, 11.3% (91/806) of dichorionic twins and 4.9% (6/122) of monochorionic twins. Multivariate logistic regression analysis demonstrated that the risk of test failure, first, increased with increasing maternal age (odds ratio (OR), 1.02; 95% CI, 1.01-1.04) and weight (OR, 1.05; 95% CI, 1.04-1.05), decreasing gestational age (OR, 0.85; 95% CI, 0.79-0.91), serum pregnancy-associated plasma protein-A (PAPP-A) multiples of the median (MoM) (OR, 0.56; 95% CI, 0.49-0.65) and free β-human chorionic gonadotropin (β-hCG) MoM (OR, 0.67; 95% CI, 0.60-0.74), second, was higher in women of black (OR, 1.72; 95% CI, 1.33-2.20) and South Asian (OR, 1.99; 95% CI, 1.56-2.52) than those of white racial origin, in dichorionic twin than in singleton pregnancy (OR, 1.75; 95% CI, 1.34-2.26) and in pregnancies conceived by in-vitro fertilization than in those conceived naturally (OR, 3.82; 95% CI, 3.19-4.55) and, third, was lower in parous than in nulliparous women (OR, 0.63; 95% CI, 0.55-0.74).

CONCLUSIONS

Maternal age, weight, racial origin and parity, gestational age, dichorionicity, method of conception and serum levels of free β-hCG and PAPP-A are independent predictors of cfDNA test failure. The risk of test failure is higher in dichorionic twin than in singleton pregnancies, mainly because a higher proportion of twins are conceived by in-vitro fertilization and more of the women are nulliparous. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.