Routine first-trimester screening for fetal trisomies in twin pregnancy: cell-free DNA test contingent on results from combined test

The Value of Nuchal Translucency (NT) Ultrasonography for Fetal Malformation Screening

BACKGROUND

Early detection of fetal malformations is crucial for timely intervention and management in obstetric care. Existing screening methods may have limitations, prompting the exploration of novel approaches to improve detection accuracy.

AIM

This retrospective study explores an efficient fetal malformation screening method, aiming to provide a reference for obstetric examination.

METHODS

A total of 511 puerperae who underwent standardized ultrasound examinations in our hospital's first trimester from December 2020 to August 2022 were enrolled. Ultrasound was used to detect the thickness of the nuchal translucency (NT) in all puerperae during prenatal examination. The clinical values of detection indices in maternal prenatal physical examination were analyzed.

RESULTS

A total of 511 puerperae were investigated, and 12 malformed fetuses were detected, presenting a fetal malformation rate of 2.35%, including 3 cases of head and neck hydrocele, 2 cases of megacystis, 3 cases of anencephaly, and 4 cases of omphalocele. Among 499 normal fetuses, NT thickness > 3.0 mm accounted for 3.41%, while among the 12 malformed fetuses screened, NT thickness > 3.0 mm accounted for 75.00%, and there was a statistical difference between the two groups (Chi-square = 124.374, P < 0.05). Using ultrasound for fetal malformation screening revealed that the fetus with NT thickness value above 3.0 mm performed better in ultrasound screening (>3.0: AUC of 0.904; >3.5: AUC of 0.928; >4.0: AUC of 0.944 vs. >2.0: AUC of 0.863; >2.5: AUC of 0.878).

CONCLUSION

The findings underscore the critical clinical significance of NT thickening as a promising ultrasound soft index for screening fetal malformations. Beyond aiding in clinical diagnosis and postpartum treatment, the potential applications of these findings hold immense practical value. They pave the way for enhanced prenatal and postnatal care practices, emphasizing the translation of research outcomes into tangible benefits for healthcare providers and expectant parents alike.

The role of ultrasound in first-trimester screening after the introduction of NIPT as a service of public health insurance - a consensus statement of the Fetal Medicine Foundation (FMF) Germany

Combined first-trimester screening (FTS) and noninvasive prenatal testing (NIPT) have been proven to be reliable noninvasive procedures to detect the most common chromosomal abnormalities (trisomies 21, 18, 13) in the first trimester. The aim of this paper is to demonstrate the strengths and limitations of these two procedures and to give a consensus statement of the Fetal Medicine Foundation (FMF) Germany on how to use the two techniques in the first trimester after the introduction of NIPT as a service of the statutory health insurance companies in Germany.

A novel artificial intelligence model for fetal facial profile marker measurement during the first trimester

BACKGROUND

To study the validity of an artificial intelligence (AI) model for measuring fetal facial profile markers, and to evaluate the clinical value of the AI model for identifying fetal abnormalities during the first trimester.

METHODS

This retrospective study used two-dimensional mid-sagittal fetal profile images taken during singleton pregnancies at 11-13+ 6 weeks of gestation. We measured the facial profile markers, including inferior facial angle (IFA), maxilla-nasion-mandible (MNM) angle, facial-maxillary angle (FMA), frontal space (FS) distance, and profile line (PL) distance using AI and manual measurements. Semantic segmentation and landmark localization were used to develop an AI model to measure the selected markers and evaluate the diagnostic value for fetal abnormalities. The consistency between AI and manual measurements was compared using intraclass correlation coefficients (ICC). The diagnostic value of facial markers measured using the AI model during fetal abnormality screening was evaluated using receiver operating characteristic (ROC) curves.

RESULTS

A total of 2372 normal fetuses and 37 with abnormalities were observed, including 18 with trisomy 21, 7 with trisomy 18, and 12 with CLP. Among them, 1872 normal fetuses were used for AI model training and validation, and the remaining 500 normal fetuses and all fetuses with abnormalities were used for clinical testing. The ICCs (95%CI) of the IFA, MNM angle, FMA, FS distance, and PL distance between the AI and manual measurement for the 500 normal fetuses were 0.812 (0.780-0.840), 0.760 (0.720-0.795), 0.766 (0.727-0.800), 0.807 (0.775-0.836), and 0.798 (0.764-0.828), respectively. IFA clinically significantly identified trisomy 21 and trisomy 18, with areas under the ROC curve (AUC) of 0.686 (95%CI, 0.585-0.788) and 0.729 (95%CI, 0.621-0.837), respectively. FMA effectively predicted trisomy 18, with an AUC of 0.904 (95%CI, 0.842-0.966). MNM angle and FS distance exhibited good predictive value in CLP, with AUCs of 0.738 (95%CI, 0.573-0.902) and 0.677 (95%CI, 0.494-0.859), respectively.

CONCLUSIONS

The consistency of fetal facial profile marker measurements between the AI and manual measurement was good during the first trimester. The AI model is a convenient and effective tool for the early screen for fetal trisomy 21, trisomy 18, and CLP, which can be generalized to first-trimester scanning (FTS).

First Trimester Screening - Current Status and Future Prospects After Introduction of Non-invasive Prenatal Testing (NIPT) at a Tertiary Referral Center

Objective To investigate the uptake of different components of first trimester screening (FTS) and the impact on invasive diagnostic testing (IPT) since the introduction of non-invasive prenatal testing (NIPT) at a level III center. Methods Retrospective data analysis was conducted for singleton pregnancies that presented for FTS between 01/2019-12/2019 (group 1, n = 990). Patients were categorized into three risk groups: low risk for trisomy 21 (< 1 : 1000), intermediate risk (1 : 101-1 : 1000) and high risk (≥ 1 : 100). Uptake of NIPT and IPT was analyzed for each of the risk groups. Results were compared to a previous cohort from 2012/2013 (immediately after the introduction of NIPT, group 2, n = 1178). Results Group 1 showed a significant increase in the use of NIPT as part of FTS (29.5% vs. 3.7% for group 2, p = 0.001) in all three risk groups. Overall IPT rates were lower in group 1 (8.6%) vs. group 2 (11.3%, p = 0.038), mainly due to a significant reduction of IPT in the intermediate risk group. IPT rates in the high-risk group remained stable over time. Conclusion Appropriate clinical implementation of NIPT is still currently a challenge for prenatal medicine experts. Our data suggest that widespread uptake of NIPT is becoming more common these days; however, a contingent approach might prevent redundant uptake.

Future Perspectives in Oxidative Stress in Trisomy 13 and 18 Evaluation

Autosomal aneuploidies are the most frequently occurring congenital abnormalities and are related to many metabolic disorders, hormonal dysfunctions, neurotransmitter abnormalities, and intellectual disabilities. Trisomies are generated by an error of chromosomal segregation during cell division. Accumulating evidence has shown that deregulated gene expression resulting from the triplication of chromosomes 13 and 18 is associated with many disturbed cellular processes. Moreover, a disturbed oxidative stress status may be implicated in the occurrence of fetal malformations. Therefore, a literature review was undertaken to provide novel insights into the evaluation of trisomy 13 (T13) and 18 (T18) pathogeneses, with a particular concern on the oxidative stress. Corresponding to the limited literature data focused on factors leading to T13 and T18 phenotype occurrence, the importance of oxidative stress evaluation in T13 and T18 could enable the determination of subsequent disturbed metabolic pathways, highlighting the related role of mitochondrial dysfunction or epigenetics. This review illustrates up-to-date T13 and T18 research and discusses the strengths, limitations, and possible directions for future studies. The progressive unification of trisomy-related research protocols might provide potential medical targets in the future along with the implementation of the foundation of modern prenatal medicine.

Cell-free DNA testing of maternal blood in screening for trisomies in twin pregnancy: updated cohort study at 10-14 weeks and meta-analysis

OBJECTIVE

To expand the limited knowledge on cell-free DNA (cfDNA) analysis of maternal blood for trisomies 21, 18 and 13 in twin pregnancy by updating the data from The Fetal Medicine Foundation (FMF) on prospective first-trimester screening and those identified in a systematic review of the literature.

METHODS

The FMF data were derived from prospective screening for trisomies 21, 18 and 13 in twin pregnancies at 10 + 0 to 14 + 1 weeks' gestation using the Harmony® prenatal test. A search of MEDLINE, EMBASE, CENTRAL (The Cochrane Library), ClinicalTrials.gov and the International Clinical Trials Registry Platform (World Health Organization) was carried out to identify all peer-reviewed publications on clinical validation or implementation of maternal cfDNA testing for trisomies 21, 18 and 13 in twin pregnancy, irrespective of gestational age at testing, in which data on pregnancy outcome were provided for at least 85% of the study population. Meta-analysis was performed using the FMF data and data from the studies identified by the literature search. This review was registered in the PROSPERO international database for systematic reviews RESULTS: In the FMF study, cfDNA testing was carried out in 1442 twin pregnancies and a result was obtained, after first or second sampling, in 1367 (94.8%) cases. In 93.1% (1272/1367) of cases, there was prenatal or postnatal karyotyping or birth of phenotypically normal babies; 95 cases were excluded from further analysis either because the pregnancy ended in termination, miscarriage or stillbirth with no known karyotype (n = 56) or there was loss to follow-up (n = 39). In the 1272 pregnancies included in the study, there were 20 cases with trisomy 21, 10 with trisomy 18, two with trisomy 13 and 1240 without trisomy 21, 18 or 13. The cfDNA test classified correctly 19 (95.0%) of the 20 cases of trisomy 21, nine (90.0%) of the 10 cases of trisomy 18, one (50.0%) of the two cases of trisomy 13 and 1235 (99.6%) of the 1240 cases without any of the three trisomies. The literature search identified 12 relevant studies, excluding our papers because their data are included in the current study. In the combined populations of our study and the 12 studies identified by the literature search, there were 137 trisomy-21 and 7507 non-trisomy-21 twin pregnancies; the pooled weighted detection rate (DR) and false-positive rate (FPR) were 99.0% (95% CI, 92.0-99.9%) and 0.02% (95% CI, 0.001-0.43%), respectively. In the combined total of 50 cases of trisomy 18 and 6840 non-trisomy-18 pregnancies, the pooled weighted DR and FPR were 92.8% (95% CI, 77.6-98.0%) and 0.01% (95% CI, 0.00-0.44%), respectively. In the combined total of 11 cases of trisomy 13 and 6290 non-trisomy-13 pregnancies, the pooled weighted DR and FPR were 94.7% (95% CI, 9.14-99.97%) and 0.10% (95% CI, 0.03-0.39%), respectively.

CONCLUSIONS

In twin pregnancy, the reported DR of trisomy 21 by cfDNA testing is high, but lower than that in singleton pregnancy, whereas the FPR appears to be equally low. The number of cases of trisomy 18 and more so trisomy 13 was too small for accurate assessment of the predictive performance of the cfDNA test. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Application of an individualized nomogram in first-trimester screening for trisomy 21

OBJECTIVES

To develop and validate a nomogram based on fetal nuchal translucency thickness (NT) and ultrasonographic facial markers for screening for trisomy 21 in the first trimester of pregnancy.

METHODS

This was a retrospective case-control study using stored two-dimensional midsagittal fetal profile images captured at 11 + 0 to 13 + 6 weeks' gestation in singleton pregnancies. We included images from 302 trisomy-21 pregnancies and 322 euploid pregnancies. Cases were divided into a training set (200 euploid + 200 with trisomy 21) and a validation set (122 euploid + 102 with trisomy 21) at a ratio of approximately 2:1. For each, the maternal age, gestational age, fetal NT and karyotype were noted, and 12 ultrasonographic fetal facial markers were measured. The least absolute shrinkage and selection operator (LASSO) method and multivariable analysis were used to select automatically the discriminative markers. Logistic regression was used to develop a LASSO model, based on the selected markers, to screen for trisomy 21 in the first trimester of pregnancy. Furthermore, 60 of the 624 images were selected randomly as a retest set to evaluate the model's robustness. The predictive performance of screening for trisomy 21 of a model based on fetal NT and maternal age and of the LASSO model was assessed using the area under the receiver-operating-characteristics curve (AUC). A nomogram was developed as an individualized tool to predict patient-specific probability for trisomy 21, which is a more visual presentation of the LASSO model. The performance of the nomogram was assessed using the C-index and calibration curve.

RESULTS

Into the LASSO model were incorporated eight markers, including fetal NT, prenasal-thickness-to-nasal-bone-length ratio, facial profile line, frontomaxillary facial angle, frontonasal facial angle, mandibulomaxillary facial angle, maxilla-nasion-mandible angle and d2 (distance between the anterior edge of the prefrontal skin and the mandibulomaxillary line) (all P < 0.05). The AUCs of the LASSO model for screening for trisomy 21 were 0.983 (95% CI, 0.971-0.994) in the training set and 0.979 (95% CI, 0.966-0.993) in the validation set, and these were higher than the AUCs of all eight individual ultrasonographic markers included in the model. The AUC of the LASSO model in the retest set was 0.997 (95% CI, 0.990-1.000), indicating good robustness of the LASSO model. The AUC of the LASSO model was significantly higher than that of the model based on fetal NT and maternal age in both training and validation sets (P < 0.001 for both). The nomogram of the LASSO model showed good discrimination of trisomy 21, with C-indices of 0.983 in the training set and 0.981 in the validation set.

CONCLUSIONS

We present an individualized nomogram which incorporates fetal NT and a series of ultrasonographic facial profile markers selected by the LASSO method and multivariable analysis. This nomogram can potentially be utilized as a convenient and effective tool in screening for trisomy 21 in the first trimester of pregnancy. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Factors associated with test failure in pregnant women undergoing cell-free DNA-based testing for fetal trisomy

OBJECTIVE

To investigate the factors associated with cell-free DNA test failure, and the optimal subsequent management of these pregnancies.

METHODS

This was a retrospective study of 27,363 singleton pregnancies undergoing cell-free DNA testing. Women with cell-free DNA test failure were divided into a high-risk group and a low-risk group according to their indications. The subsequent management and pregnancy outcomes of these women were followed up.

RESULTS

The rate of cell-free DNA test failure at the first sampling was 1.49%, and 78.4% of failures were due to a low fetal fraction. Of the 66 women who refused any subsequent management, an adverse pregnancy outcome was seen in 5 cases, all belonging to the high-risk group. Of the 13 low-risk women who chose second-trimester maternal serum screening, all obtained a low-risk maternal serum screening result and an unaffected pregnancy outcome. A redraw was chosen by 171 women, which yielded a result in 75.4% and their pregnancy outcomes were unaffected; 42 women had an uninformative result again and received an amniocentesis. As 158 women had an amniocentesis after the first sampling, this procedure was offered in 200 cases altogether. Abnormal genetic testing results were shown in six (3%, 6/200) cases, all in the high-risk group.

CONCLUSIONS

High-risk pregnant women with cell-free DNA test failure are at increased risk of adverse pregnancy outcomes. A second sampling for cell-free DNA test or maternal serum screening might be suggested to low-risk women. Invasive prenatal diagnosis should be offered to the high-risk patients, especially those with a second cell-free DNA test failure.

Clinical Utility of Increased Nuchal Translucency at 11-13 Weeks of Gestation in Twin Pregnancies Based on the Chorionicity

To assess clinical implications of increased nuchal translucency (INT) in twin pregnancies based on the chorionicity. This was a retrospective review of the twin pregnancies who underwent first trimester ultrasound with nuchal translucency (NT) measurement at 11-13 weeks of gestation from January 2006 to December 2014. Data were collected using the OB database and the chart review. Pregnancy outcomes, including gestational weeks at the delivery, abnormal fetal karyotypes, fetal structural anomalies, and twin-specific complications, were analyzed. A total of 1622 twin pregnancies with INT ≥ 95th percentile in one or both fetuses were identified. In all twin pregnancies with INT, abnormal fetal karyotypes were identified in 17 (8.6%) patients (odds ratio = 13.28, CI = 5.990-29.447, p = 0.000) and twin-specific complications were identified in 23 (11.6%) patients (odds ratio = 2.398, CI = 1.463-3.928, p = 0.001) compared to those with normal NT. Among the INT group, when the groups were subdivided into monochorionic (MC) and dichorionic (DC) pregnancies, 14.8% and 29.6% of the MC pregnancies had structural anomalies in one or both fetuses (odds ratio = 5.774, 95% CI = 1.445-23.071, p = 0.01) and twin-specific complications (odds ratio = 4.379, 95% CI = 1.641-11.684, p = 0.03), respectively, compared to DC pregnancies with 2.9% for structural anomalies and 8.8% for twin-specific complications. The prevalence of abnormal fetal karyotypes was not statistically different in patients with INT when compared between MC and DC pregnancies (p = 0.329). INT was associated with a higher rate of twin-specific complications and fetal structural anomalies in MC twin pregnancies rather than abnormal fetal karyotype. Therefore, NT measurement in MC twin pregnancies can be a useful tool for predicting adverse pregnancy outcomes. Appropriate counseling and surveillance based on the chorionicity are imperative in the prenatal care of twin pregnancies.

The Significance of Apolipoprotein E Measurement in the Screening of Fetal Down Syndrome

Prenatal screening for Down syndrome (DS) is based on both noninvasive and invasive methods. Noninvasive, cell-free fetal DNA genetic tests are expensive, whereas biochemical methods remain imprecise. Amniocentesis is the most frequently used invasive diagnosis procedure, characterized by 99.8% diagnostic efficiency and less than 1% risk of miscarriage. The aim of this study was to evaluate the screening value of apolipoprotein E (ApoE) as a potential noninvasive biomarker for prenatal DS assessment. This study was conducted on a group of female patients who decided to undergo routine amniocentesis between the 15th and 18th week of pregnancy at the Department of Reproduction and Gynecological Endocrinology of the Medical University of Bialystok, Poland. For the purpose of this study, 20 women with DS fetuses were selected as the study group, and 20 healthy pregnant women with euploid fetus karyotypes as the control group. The plasma levels of ApoE were significantly higher in the study group compared to healthy subjects (p < 0.05). The area under the receiver operating characteristic (ROC) curve was 0.978 (p < 0.001), with the cut-off set to 1.37 mg/mL, which was characterized by 80% of sensitivity and 100% of specificity. The high sensitivity and specificity demonstrate the screening utility of maternal ApoE concentration in prenatal fetal DS screening.

Performance of first trimester screening for Trisomy 21 in twin pregnancies

OBJECTIVES

To assess the performance of the Danish first trimester screening program in twin pregnancies.

METHOD

Retrospective, nation-wide, cohort study with data collected from the Danish Fetal Medicine Database (DFMD) and The Danish Central Cytogenetic Registry (DCCR). The cohort included all women with twin pregnancies participating in the national first trimester screening program for Trisomy 21. Risk assessment was based on maternal age, nuchal translucency (NT) thickness and, if available, biochemical markers (β-hCG and PAPP-A).

RESULTS

8812 twin pregnancies including 42 pregnancies with Trisomy 21 had a risk assessment between 2009 and 2017. The detection rate (DR) for pregnancies with a risk assessment based on maternal age and NT only (missing data on biochemical markers, n = 4693) was 69.6% (95% CI: 50.8%-88.4%) for a 6.3% false positive rate (FPR) (95% CI: 5.6%-7.0%), whereas for pregnancies with a risk assessment based on all three parameters (n = 4119) the DR was 89.5% (95% CI: 76.7%-100.0%) for a 7.2% FPR (95% CI: 6.4%-8.0%).

CONCLUSION

The DR of Trisomy 21 in twin pregnancies, seems as high as for singleton pregnancies, when using optimal screening techniques, but the FPR is nearly twice as high.

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.

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.

First-trimester screening-biomarkers and cell-free DNA

Background: The introduction of cell-free DNA into clinical practice has changed the screening approach. Healthcare professionals and future parents tend to overestimate NIPT (noninvasive prenatal testing) capabilities despite its relatively high cost and limited information.Objective: In this review, our aim was to survey how various countries have introduced contingent screening models and to discuss the advantages and disadvantages of the combined screening test and the use of NIPT.Data source: The Web of Science, PubMed database and institutional websites were searched for information regarding screening approaches and the implementation in different countries.Results: There are nine countries and regions that have already approved contingent screening test, while others (e.g. Australia) are discussing the implementation of contingent screening versus universal use of NIPT. There are several recent meta-analyses debating whether to use NIPT for universal screening for trisomies and other fetal conditions.Conclusions: NIPT is a reasonable option as an advanced screening test for trisomy 21, 18 and 13 only. Introducing screening by NIPT instead of a first-trimester screening will cause the loss of other valuable information including accurate dating of pregnancy, diagnosing major structural fetal abnormalities and multiple pregnancies at an early gestational age. Additionally, the opportunity to screen for early preeclampsia will be lost. Currently, the price for NIPT is still high adding extra strain on publicly funded health systems.

Noninvasive prenatal testing: from aneuploidy to single genes

Noninvasive prenatal testing has undergone rapid advances in the last few years. Although researchers have long known about circulating pregnancy-based cell-free fragments of DNA in maternal plasma, it was the introduction of massively parallel sequencing that allowed noninvasive prenatal testing to become a widely used clinical test. This review will begin with an in-depth analysis of the use of noninvasive prenatal testing for aneuploidy, including common causes for inaccurate and/or discordant results. It will also review the ongoing expansion of noninvasive prenatal testing to include copy number variants and select single-gene disorders. Finally, integrated throughout the review is a comparison of noninvasive prenatal testing to more traditional screening methods along with some medical and ethical implications of the widespread use of this new technology.

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.

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

OBJECTIVES

To report on the routine clinical implementation of cell-free DNA (cfDNA) analysis of maternal blood for trisomies 21, 18 and 13 in twin pregnancy and to define the performance of the test by combining our results with those identified in a systematic review of the literature.

METHODS

The data for the prospective study were derived from screening for trisomies 21, 18 and 13 in twin pregnancies at 10 + 0 to 14 + 1 weeks' gestation. Two populations were included; first, self-referred women to the Fetal Medicine Centre in London or Brugmann University Hospital in Brussels and, second, women selected for the cfDNA test after routine first-trimester combined testing at one of two National Health Service hospitals in England. This dataset was used to determine the performance of screening for the three trisomies. Search of MEDLINE, EMBASE, CENTRAL (The Cochrane Library), ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform (ICTRP) was carried out to identify all peer-reviewed publications on clinical validation or implementation of maternal cfDNA testing for trisomies 21, 18 and 13 in twin pregnancy. A meta-analysis was then performed using our data and those in the studies identified by the literature search.

RESULTS

In our dataset of 997 twin pregnancies with a cfDNA result and known outcome, the test classified correctly 16 (94.1%) of the 17 cases of trisomy 21, nine (90.0%) of the 10 cases of trisomy 18, one (50.0%) of the two cases of trisomy 13 and 962 (99.4%) of the 968 cases without any of the three trisomies. The literature search identified seven relevant studies, excluding our previous papers because their data are included in the current study. In the combined populations of our study and the seven studies identified by the literature search, there were 56 trisomy-21 and 3718 non-trisomy-21 twin pregnancies; the pooled weighted detection rate (DR) and false-positive rate (FPR) were 98.2% (95% CI, 83.2-99.8%) and 0.05% (95% CI, 0.01-0.26%), respectively. In the combined total of 18 cases of trisomy 18 and 3143 non-trisomy-18 pregnancies, the pooled weighted DR and FPR were 88.9% (95% CI, 64.8-97.2%) and 0.03% (95% CI, 0.00-0.33%), respectively. For trisomy 13, there were only three affected cases and two (66.7%) of these were detected by the cfDNA test at a FPR of 0.19% (5/2569).

CONCLUSIONS

The performance of cfDNA testing for trisomy 21 in twin pregnancy is similar to that reported in singleton pregnancy and is superior to that of the first-trimester combined test or second-trimester biochemical testing. The number of cases of trisomies 18 and 13 is too small for accurate assessment of the predictive performance of the cfDNA test. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.