International Society for Prenatal Diagnosis Position Statement: cell free (cf)DNA screening for Down syndrome in multiple pregnancies

The efficacy of expanded non-invasive prenatal testing (NIPT) in a high-risk twin pregnancies cohort

INTRODUCTION

Our objective was to evaluate the efficacy of expanded non-invasive prenatal testing (NIPT) that includes both trisomies and copy number variants (CNVs) in high-risk twin pregnancies.

MATERIAL AND METHODS

A prospective, double-blinded cohort study was conducted, enrolling 73 high-risk twin pregnancies characterized by increased risk of genetic disorders due to factors such as increased nuchal translucency, structural anomalies, fetal growth restriction, and other factors associated with chromosomal abnormality. Participants underwent invasive karyotyping and chromosomal microarray analysis, alongside separate expanded NIPT for research purposes. The sensitivity, specificity, positive predictive value, and negative predictive value of expanded NIPT were calculated.

RESULTS

The cohort included 24 monochorionic and 49 dichorionic twin pregnancies. The median cell-free fetal DNA concentration in expanded NIPT was 16.7% (range 3.86%-49.1%), with a test failure rate of 1.4% (1/73). High-risk findings for trisomy 21/13/18 were identified in five cases (6.8%), Turner syndrome in one case (1.4%), and CNVs indicative of high risk for clinically significant microdeletion/microduplication syndromes (MMS) in ten cases (13.7%). Of these, 56 cases (76.7%) tested NIPT negative, revealing one false-negative for 45, X and five false-negatives for CNVs. Expanded NIPT achieved a detection rate of 100% (5/5) for trisomy 21/13/18 with a false-positive rate of 0% (0/5), a detection rate of 33.3% (1/3) for sex chromosome abnormalities with a false-positive rate of 0% (0/3), and a detection rate of 66.7% (4/6) for MMS with a false-positive rate of 3.0% (2/67). The positive predictive values for trisomy T21/13/18, sex chromosome abnormalities, and known MMS were 100% (5/5), 100% (1/1), and 66.7% (4/6) in the expanded NIPT, respectively.

CONCLUSIONS

The expanded NIPT demonstrated high detection rates for common trisomies and moderate detection rates for prenatal MMS in high-risk twin pregnancies. Further studies with large sample sizes in low-risk populations are needed.

Noninvasive twin genotyping for recessive monogenic disorders by relative haplotype dosage

OBJECTIVE

To establish a haplotype-based noninvasive prenatal testing (NIPT) workflow for single-gene recessive disorders that adapt to dizygotic (DZ) twin pregnancies.

METHOD

Twin pregnancies at risk of Duchenne muscular dystrophy, Becker muscular dystrophy, hemophilia B, spinal muscular atrophy, phenylketonuria, and nonsyndromic hearing loss were recruited. For subsequent analysis, capture sequencing targeting highly heterozygotic single nucleotide polymorphism sites was conducted. Paternal-specific alleles were used to calculate the total and individual fetal fractions and determine zygosity. A two-step Bayes Factor model was applied to clarify the complex genomic landscape in the maternal plasma: the first step involved determining whether the twins inherited the same haplotype, and the second step involved estimating their individual genotypes. NIPT results were subsequently confirmed by invasive diagnosis.

RESULTS

Nine twin pregnancies were recruited, including five DZ and four monozygotic (MZ) twins. The earliest gestational age was 8+0 weeks, and the minimum fetal fraction was 4.6%. Three twin pregnancies were reported with one affected fetus, while the remaining six were reported without affected fetuses. Two dichorionic diamniotic twin pregnancies were confirmed to be MZ twins. The NIPT results were 100% consistent with those of invasive procedures or diagnostic genetic testing after birth.

CONCLUSION

This study is the first to perform NIPT for single-gene disorders in twin pregnancies and preliminarily confirm its clinical feasibility. Acknowledging the twins' genotypes in the first trimester is valuable as it empowers obstetric care providers and parents to have adequate time for pregnancy management and decision-making.

Non-invasive cell-free DNA prenatal screening for trisomy 21 as part of primary screening strategy in twin pregnancy

OBJECTIVES

The performance of non-invasive prenatal screening using cell-free DNA testing of maternal blood in twin pregnancy is underevaluated, while serum marker-based strategies yield poor results. This study aimed to assess the performance of non-invasive prenatal screening for trisomy 21 in twin pregnancy as a first-tier test. Secondary objectives were to assess its failure rate and factors associated with failure.

METHODS

This retrospective cohort study included twin pregnancies in which non-invasive prenatal screening using cell-free DNA was performed as the primary screening strategy between May 2017 and October 2019. We used the NIPT VeriSeq® test for in-vitro diagnosis and set a fetal fraction cut-off of 4% for monochorionic pregnancies and 8% for dichorionic ones. Clinical data and pregnancy outcome were collected from physicians or midwives via a questionnaire or were retrieved directly on-site. We calculated the performance of non-invasive cell-free DNA screening for trisomy 21, analyzed its failure rate and assessed potentially associated factors.

RESULTS

Among 1885 twin pregnancies with follow-up, there were six (0.32%) confirmed cases of trisomy 21. The sensitivity of non-invasive prenatal screening for trisomy 21 was 100% (95% CI, 54.1-100%) and the false-positive rate was 0.23% (95% CI, 0.06-0.59%). The primary failure rate was 4.6%, with 4.0% being due to insufficient fetal fraction. A successful result was obtained for 65.4% of women who underwent a new blood draw, reducing the overall failure rate to 2.8%. Maternal body mass index, gestational age at screening as well as chorionicity were significantly associated with the risk of failure.

CONCLUSION

This study provides further evidence of the high performance, at an extremely low false-positive rate, of non-invasive prenatal screening in twins as part of a primary screening strategy for trisomy 21. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Performance of cell-free DNA testing for common fetal trisomies in triplet pregnancies

OBJECTIVE

In singleton pregnancies, the use of cell-free DNA (cfDNA) analysis as a screening test for common fetal trisomies has spread worldwide though we still lack sufficient data for its use in triplet pregnancies. The objective of this study is to assess the performance of cfDNA testing in detecting fetal aneuploidies in triplet pregnancies as a first-tier test.

METHOD

We performed a retrospective cohort study including data from pregnant women with a triplet pregnancy who underwent cfDNA testing between May 1, 2017, and January 15, 2020. cfDNA was obtained by massive parallel sequencing (VeriSeq NIPT solution; Illumina®). The objectives of the study were to assess the diagnostic performance of cfDNA testing for trisomy 21 (T21) (primary outcome), trisomy 18 (T18) and 13 (secondary outcomes).

RESULTS

During the study period, cfDNA testing was performed in 255 women with triplet pregnancy, of which 165 (64.7%) had a neonatal outcome available. Three tests were positive for T21, one of which was confirmed by an antenatal karyotype, and the other was confirmed at birth. The third case did not undergo an invasive procedure and was not confirmed at birth (false positive). In one case, cfDNA testing was positive for T18 and was confirmed by an antenatal karyotype. There were no cases of trisomy 13 in the cohort. The no-call rate was 2.4% at first sampling. Fifty-eight (22.7%) women had embryo reduction, which in 40 (69%) of whom was performed after the cfDNA test result.

CONCLUSION

cfDNA testing could be offered as primary screening for main fetal aneuploidies in triplet pregnancies after provision of appropriate patient information.

Clinical Experience with Noninvasive Prenatal Testing in Twin Pregnancy Samples at a Single Center in Germany

In this study we wanted to determine the performance of a paired-end sequencing-based noninvasive prenatal testing (NIPT) assay in the detection of common fetal trisomies in twin pregnancy samples. Samples from patients with a twin pregnancy were collected from at least 10 weeks of gestation and analyzed at a single prenatal center in Germany. Results of Anomaly Detected (i.e., high risk) or No Anomaly Detected (i.e., low risk) for trisomy 21, trisomy 18, or trisomy 13 were reported. Follow-up confirmatory outcomes were requested for all cases. A total of 1,658 patients with twin pregnancies submitted samples during the study period; only two of these samples failed resulting in a low failure rate of 0.12%. Of the remaining 1,656 cases, there were 1,625 (98.1%) low-risk and 31 (1.9%) high-risk NIPT samples in our cohort. Of these, follow-up information was available for 301 (18.5%) of the low-risk samples and 19 (61.3%) of the high-risk samples. All of the low-risk cases with follow-up were determined to be true negatives giving an estimated negative predictive value of 100%. Seventeen of the 19 high-risk samples with follow-up were true positives, resulting in an overall positive predictive value of 89.5%. Sensitivities of > 99.9% were noted for both trisomy 21 and trisomy 18, with high specificities of ≥ 99.7% observed for all three trisomies. In conclusion, our study showed strong performance of the NIPT assay in the detection of common fetal trisomies in twin pregnancy samples, with high sensitivities, specificities, and positive predictive values observed based on known clinical outcomes along with a low failure rate.

National and international guidelines on the management of twin pregnancies: a comparative review

Twin gestations are associated with increased risk of pregnancy complications. However, high-quality evidence regarding the management of twin pregnancies is limited, often resulting in inconsistencies in the recommendations of various national and international professional societies. In addition, some recommendations related to the management of twin gestations are often missing from the clinical guidelines dedicated to twin pregnancies and are instead included in the practice guidelines on specific pregnancy complications (eg, preterm birth) of the same professional society. This can make it challenging for care providers to easily identify and compare recommendations for the management of twin pregnancies. This study aimed to identify, summarize, and compare the recommendations of selected professional societies from high-income countries on the management of twin pregnancies, highlighting areas of both consensus and controversy. We reviewed clinical practice guidelines of selected major professional societies that were either specific to twin pregnancies or were focused on pregnancy complications or aspects of antenatal care that may be relevant for twin pregnancies. We decided a priori to include clinical guidelines from 7 high-income countries (United States, Canada, United Kingdom, France, Germany, and Australia and New Zealand grouped together) and from 2 international societies (International Society of Ultrasound in Obstetrics and Gynecology and the International Federation of Gynecology and Obstetrics). We identified recommendations regarding the following care areas: first-trimester care, antenatal surveillance, preterm birth and other pregnancy complications (preeclampsia, fetal growth restriction, and gestational diabetes mellitus), and timing and mode of delivery. We identified 28 guidelines published by 11 professional societies from the 7 countries and 2 international societies. Thirteen of these guidelines focus on twin pregnancies, whereas the other 16 focus on specific pregnancy complications predominantly in singletons but also include some recommendations for twin pregnancies. Most of the guidelines are recent, with 15 of the 29 guidelines published over the past 3 years. We identified considerable disagreement among guidelines, primarily in 4 key areas: screening and prevention of preterm birth, using aspirin to prevent preeclampsia, defining fetal growth restriction, and the timing of delivery. In addition, there is limited guidance on several important areas, including the implications of the "vanishing twin" phenomenon, technical aspects and risks of invasive procedures, nutrition and weight gain, physical and sexual activity, the optimal growth chart to be used in twin pregnancies, the diagnosis and management of gestational diabetes mellitus, and intrapartum care.This consolidation of key recommendations across several clinical practice guidelines can assist healthcare providers in accessing and comparing recommendations on the management of twin pregnancies and identifies high-priority areas for future research based on either continued disagreement among societies or limited current evidence to guide care.

Non-invasive prenatal testing: a revolutionary journey in prenatal testing

Non-invasive prenatal testing (NIPT) is a pioneering technique that has consistently advanced the field of prenatal testing to detect genetic abnormalities and conditions with the aim of decreasing the incidence and prevalence of inherited conditions. NIPT remains a method of choice for common autosomal aneuploidies, mostly trisomy 21, and several monogenic disorders. The advancements in gene sequencing techniques have expanded the panel of conditions where NIPT could be offered. However, basic research on the impact of several genetic conditions lags behind the methods of detection of these sequence aberrations, and the impact of the expansion of NIPT should be carefully considered based on its utility. With interest from commercial diagnostics and a lack of regulatory oversight, there remains a need for careful validation of the predictive values of different tests offered. NIPT comes with many challenges, including ethical and economic issues. The scientific evidence, technical feasibility, and clinical benefit of NIPT need to be carefully investigated before new tests and developments are translated into clinical practice. Moreover, the implementation of panel expansion of NIPT should accompany expert genetic counseling pre- and post-testing.

Overview of Noninvasive Prenatal Testing (NIPT) for the Detection of Fetal Chromosome Abnormalities; Differences in Laboratory Methods and Scope of Testing

Although nearly all noninvasive prenatal testing is currently based on analyzing circulating maternal cell-free DNA, the technical methods usedvary considerably. We review the different methods. Based on validation trials and clinical experience, there are mostly relatively small differences in screening performance for trisomies 21, 18, and 13 in singleton pregnancies. Recent reports show low no-call rates for all methods, diminishing its importance when choosing a laboratory. However, method can be an important consideration for twin pregnancies, screening for sex chromosome abnormalities, microdeletion syndromes, triploidy, molar pregnancies, rare autosomal trisomies, and segmental imbalances, and detecting maternal chromosome abnormalities.

Performance of noninvasive prenatal testing for twin pregnancies in South China

OBJECTIVE

The purpose of this study was to evaluate the performance of noninvasive prenatal testing (NIPT) for the detection of chromosomal aneuploidies and copy number variations (CNVs) in twin pregnancies.

METHOD

A cohort of 2010 women with twin pregnancies was recruited. 1331 patients opted for NIPT, and 679 patients opted for expanded NIPT (NIPT-plus). All high-risk patients were advised to undergo invasive prenatal diagnosis. All participants were followed up until 6 months after birth.

RESULTS

Twenty-two cases were predicted to have a high risk of chromosome abnormalities by NIPT, of which 14 pregnant women underwent invasive prenatal diagnosis. The 14 cases included 3 cases of trisomy 21, 1 case of trisomy 18, 1 case of trisomy 7, 2 cases of sex chromosome aneuploidies (SCAs), and 7 cases of CNVs, of which the confirmed cases numbered 2, 1, 0, 1, and 0, respectively. Twenty cases were predicted to have a high risk of chromosome abnormalities by NIPT-plus, of which 16 pregnant women underwent invasive prenatal diagnosis. The 16 cases included 1 case of trisomy 21, 1 case of trisomy 7, 7 cases of SCAs, and 7 cases of CNVs, of which were confirmed in 1, 0, 3, and 2, respectively. No false-negative result was reported during the follow-up period.

CONCLUSION

The NIPT/NIPT-plus has excellent performance in the detection of chromosome aneuploidies in twin pregnancies. But for CNVs, the effectiveness of NIPT is poor, and the NIPT-plus have a certain detection efficiency. It is worth noting that pre- and post-genetic counseling is especially important, and the chorionicity, mode of conception, clinical indications, and fetal fraction should be considered as influencing factors.

Analysis of retest reliability for pregnant women undergoing cfDNA testing with a no-call result

BACKGROUND

Determining the reasons for unreportable or no-call cell-free DNA (cfDNA) test results has been an ongoing issue, and a consensus on subsequent management is still lacking. This study aimed to explore potential factors related to no-call cfDNA test results and to discuss whether retest results are reliable.

METHODS AND RESULTS

This was a retrospective study of women with singleton pregnancies undergoing cfDNA testing in 2021. Of the 9871 pregnant patients undergoing cfDNA testing, 111 had a no-call result, and their results were compared to those of 170 control patients. The no-call rate was 1.12% (111/9871), and the primary cause for no-call results was data fluctuation (88.29%, 98/111). Medical conditions were significantly more frequent in the no-call group than in the reportable results group (P < 0.001). After retesting, 107 (107/111, 96.40%) patients had a result, and the false-positive rate (FPR) of retesting was 10.09% (10.09%, 11/109). In addition, placental lesions were more frequent in the no-call group than in the reportable results group (P = 0.037), and 4 patients, all in the no-call group, experienced pregnancy loss.

CONCLUSIONS

Pregnant women with medical conditions are more likely to have a no-call result. A retest is suggested for patients with a no-call result, but retests have a high FPR. In addition, pregnant women with a no-call result are at increased risk of adverse pregnancy outcomes. In conclusion, more attention should be given to pregnant women for whom a no-call cfDNA result is obtained.

Directive clinique no 440 : Prise en charge de la grossesse gémellaire monochoriale

OBJECTIF

Cette directive clinique passe en revue les données probantes sur la prise en charge de la grossesse gémellaire monochoriale normale et compliquée.

POPULATION CIBLE

Les femmes menant une grossesse gémellaire ou multiple de haut rang. BéNéFICES, RISQUES ET COûTS: L'application des recommandations de cette directive devrait améliorer la prise en charge des grossesses gémellaires (ou multiples de haut rang) monochoriales compliquées et non compliquées. Ces recommandations aideront les fournisseurs de soins à surveiller adéquatement les grossesses gémellaires monochoriales ainsi qu'à détecter et prendre en charge rapidement les complications associées de façon optimale afin de réduire les risques de morbidité et mortalité périnatales. Ces recommandations impliquent une surveillance échographique plus fréquente en cas de grossesse monochoriale qu'en cas de grossesse bichoriale. DONNéES PROBANTES: La littérature publiée a été colligée par des recherches dans les bases de données PubMed et Cochrane Library au moyen de termes MeSH pertinents (Twins, Monozygotic; Ultrasonography, Prenatal; Placenta; Fetofetal Transfusion; Fetal Death; Fetal Growth Retardation). Les résultats ont été restreints aux revues systématiques, aux essais cliniques randomisés et aux études observationnelles. Aucune date limite n'a été appliquée, mais les résultats ont été limités aux contenus en anglais ou en français. MéTHODES DE VALIDATION: Les auteurs principaux ont rédigé le contenu et les recommandations et ils se sont entendus sur ces derniers. Le conseil d'administration de la SOGC a approuvé la version définitive aux fins de publication. Les auteurs ont évalué la qualité des données probantes et la force des recommandations en utilisant le cadre méthodologique GRADE (Grading of Recommendations Assessment, Development and Evaluation). Voir l'annexe A en ligne (tableau A1 pour les définitions et tableau A2 pour l'interprétation des recommandations fortes et conditionnelles [faibles]). PROFESSIONNELS CONCERNéS: Spécialistes en médecine fœto-maternelle, obstétriciens, radiologues, échographistes, médecins de famille, infirmières, sages-femmes, résidents et autres fournisseurs de soins de santé qui s'occupent de femmes menant une grossesse gémellaire ou multiple de haut rang. RéSUMé POUR TWITTER: Directive canadienne (SOGC) pour le diagnostic, la surveillance échographique et la prise en charge des complications de la grossesse gémellaire monochoriale (p. ex., STT, TAPS, retard de croissance sélectif, cojumeau acardiaque, monoamnionicité et mort d'un jumeau). DÉCLARATIONS SOMMAIRES: RECOMMANDATIONS.

Guideline No. 440: Management of Monochorionic Twin Pregnancies

OBJECTIVE

This guideline reviews the evidence-based management of normal and complicated monochorionic twin pregnancies.

TARGET POPULATION

Women with monochorionic twin or higher order multiple pregnancies.

BENEFITS, HARMS, AND COSTS

Implementation of these recommendations should improve the management of both complicated and uncomplicated monochorionic (and higher order multiple) twin pregnancies. They will help users monitor monochorionic twin pregnancies appropriately and identify and manage monochorionic twin complications optimally in a timely manner, thereby reducing perinatal morbidity and mortality. These recommendations entail more frequent ultrasound monitoring of monochorionic twins compared to dichorionic twins.

EVIDENCE

Published literature was retrieved through searches of PubMed and the Cochrane Library using appropriate MeSH headings (Twins, Monozygotic; Ultrasonography, Prenatal; Placenta; Fetofetal Transfusion; Fetal Death; Fetal Growth Retardation). Results were restricted to systematic reviews, randomized controlled clinical trials, and observational studies. There were no date limits, but results were limited to English or French language materials.

VALIDATION METHODS

The content and recommendations were drafted and agreed upon by the principal authors. The Board of the SOGC approved the final draft for publication. The authors rated the quality of evidence and strength of recommendations using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. See online Appendix A (Tables A1 for definitions and A2 for interpretations of strong and conditional [weak] recommendations).

INTENDED AUDIENCE

Maternal-fetal medicine specialists, obstetricians, radiologists, sonographers, family physicians, nurses, midwives, residents, and other health care providers who care for women with monochorionic twin or higher order multiple pregnancies.

TWEETABLE ABSTRACT

Canadian (SOGC) guidelines for the diagnosis, ultrasound surveillance and management of monochorionic twin pregnancy complications, including TTTS, TAPS, sFGR (sIUGR), acardiac (TRAP), monoamniotic twins and intrauterine death of one MC twin.

SUMMARY STATEMENTS

RECOMMENDATIONS.

Position statement from the International Society for Prenatal Diagnosis on the use of non-invasive prenatal testing for the detection of fetal chromosomal conditions in singleton pregnancies

What is already known about this topic?

What does this study add?

Clinical practice guidelines for the antenatal management of dichorionic diamniotic twin pregnancies: a systematic review

OBJECTIVE

This review aimed to identify guidelines with recommendations applicable to the antenatal management of dichorionic diamniotic twin pregnancies within high-income countries, appraise their methodological quality, and discuss the similarities and variability across guidelines.

METHOD

A systematic literature review of electronic databases was performed. Manual searches of guideline repositories and websites of professional organisations were performed to identify additional guidelines. The protocol for this systematic review was registered on PROSPERO (CRD42021248586, 25 June 2021). AGREE II and AGREE-REX tools were applied to assess the quality of eligible guidelines. A narrative and thematic synthesis described and compared the guidelines and their recommendations.

RESULTS

Twenty-four guidelines were included, from which 483 recommendations were identified across 4 international organisations and 12 countries. Guidelines addressed eight themes and recommendations were classified accordingly: chorionicity and dating (103 recommendations), fetal growth (105 recommendations), termination of pregnancy (12 recommendations), fetal death (13 recommendations), fetal anomalies (65 recommendations), antenatal care (65 recommendations), preterm labour (56 recommendations) and birth (54 recommendations). Guidelines showed significant variability in recommendations, with conflicting recommendations regarding non-invasive preterm testing, definitions surrounding selective fetal growth restriction, screening for preterm labour and the timing of birth. Guidelines lacked a focus on standard antenatal management of DCDA twins, management of discordant fetal anomaly and single fetal demise.

CONCLUSIONS

Specific guidance for dichorionic diamniotic twins is overall indistinct and access to guidance regarding the antenatal management of these pregnancies is currently difficult. Management of discordant fetal anomaly or single fetal demise needs greater consideration.

Clinical Experience with Genome-Wide Noninvasive Prenatal Screening in a Large Cohort of Twin Pregnancies

Non-invasive prenatal screening (NIPS) in twin gestations has been shown to have high detection rates and low false-positive rates for trisomy 21, as seen in singleton pregnancies, although there have been few large cohort twin studies, genome-wide studies in particular, to date. In this study, we looked at the performance of genome-wide NIPT in a large cohort consisting of 1244 twin pregnancy samples collected over a two-year period in a single laboratory in Italy. All samples underwent an NIPS for common trisomies, with 61.5% of study participants choosing to undergo genome-wide NIPS for additional fetal anomalies (namely, rare autosomal aneuploidies and CNVs). There were nine initial no-call results, all of which were resolved upon retest. Based on our NIPS results, 17 samples were at high risk for trisomy 21, one for trisomy 18, six for a rare autosomal aneuploidy, and four for a CNV. Clinical follow-up was available for 27 out of 29 high-risk cases; a sensitivity of 100%, a specificity of 99.9%, and a PPV of 94.4% were noted for trisomy 21. Clinical follow-up was also available for 1110 (96.6%) of the low-risk cases, all of which were true negatives. In conclusion, we found that NIPS was a reliable screening approach for trisomy 21 in twin pregnancies.

Can maternal serum midkine level predict chorionicity in twin pregnancies?

Sometimes it can be difficult to chorionicity determination in twin pregnancies. This study aimed to compare maternal serum midkine levels between twin and singleton pregnancies. We also evaluated the relationship between chorionicity and maternal serum midkine level in twin pregnancies. The present prospective cohort study included 16 patients with monochorionic diamniotic twin pregnancies, 38 with dichorionic diamniotic twin pregnancies, and 66 healthy singleton pregnancies admitted to Ankara City Hospital Perinatology Clinic between June 2021 and June 2022. Demographic features, clinical characteristics, and serum midkine levels were compared between the groups. Additionally, a receiver operator characteristics (ROC) analysis was performed to assess the performance of midkine for detecting chorionicity. The median maternal serum midkine level was found to be 0.64 ng/ml in twin pregnancies and 0.26 ng/ml in singleton pregnancies (p < 0.001). When twin pregnancies were compared in terms of chorionicity, serum midkine level was determined as 1.20 ng/ml in the monochorionic diamniotic group and 0.50 ng/ml in the dichorionic diamniotic group (p = 0.034). An optimal cut-off value of 1.03 ng/ml was found for the determination of chorionicity (AUC: 0.68, p = 0.03, 95% CI: 0.53-0.83, %56.3 sensitivity, 76.3% specificity). In advanced weeks of pregnancy, biomarkers can be used as helpful parameters for ultrasonography in the diagnosis of twin pregnancies. Maternal serum midkine levels might be used to determine chorionicity in equivocal cases.

Clinical application of noninvasive prenatal testing in twin pregnancies: a single-center experience

OBJECTIVES

To evaluate the clinical efficiency of noninvasive prenatal testing (NIPT) for fetal chromosomal aneuploidy screening in twin pregnancies.

METHODS

A total of 1650 women with twin pregnancies were enrolled in the study, which underwent NIPT at the Southwest Hospital, Army Medical University, Chongqing, China from January 2013 to June 2022. Fetal karyotyping analysis was conducted in high-risk patients, with subsequent follow-up on pregnancy outcomes.

RESULTS

In 1650 pregnancies, NIPT results showed ten cases of the fetal chromosome aneuploidy, of which six cases were true positive and four cases were false positive. The sensitivity, specificity, positive predictive value (PPV), and false-positive rate (FPR) of trisomy 21 were 100%, 99.79%, 57.14%, and 0.18%, respectively. Sensitivity, specificity, PPV, and FPR of trisomy 18 were 100%, 99.94%, 50%, and 0.06%, respectively. The sensitivity, specificity, PPV, and FPR of trisomy 13 were 100%, 100%, 100%, and 0%, respectively. No false negatives were detected and the negative predictive value (NPV) was 100% of the total. Eleven pregnancies failed the NIPT test with no-call due to the low fetal fraction (< 4%).

CONCLUSIONS

NIPT is a high-performing routine primary prenatal screening test in twin pregnancies, with high sensitivity and specificity in screening for fetal aneuploidy.

Isolation of single circulating trophoblasts from maternal circulation for noninvasive fetal copy number variant profiling

OBJECTIVE

To develop a multi-step workflow for the isolation of circulating extravillous trophoblasts (cEVTs) by describing the key steps enabling a semi-automated process, including a proprietary algorithm for fetal cell origin genetic confirmation and copy number variant (CNV) detection.

METHODS

Determination of the limit of detection (LoD) for submicroscopic CNV was performed by serial experiments with genomic DNA and single cells from Coriell cell line biobank with known imbalances of different sizes. A pregnancy population of 372 women was prospectively enrolled and blindly analyzed to evaluate the current workflow.

RESULTS

An LoD of 800 Kb was demonstrated with Coriell cell lines. This level of resolution was confirmed in the clinical cohort with the identification of a pathogenic CNV of 800 Kb, also detected by chromosomal microarray. The mean number of recovered cEVTs was 3.5 cells per sample with a significant reverse linear trend between gestational age and cEVT recovery rate and number of recovered cEVTs. In twin pregnanices, evaluation of zygosity, fetal sex and copy number profiling was performed in each individual cell.

CONCLUSION

Our semi-automated methodology for the isolation and single-cell analysis of cEVTS supports the feasibility of a cell-based noninvasive prenatal test for fetal genomic profiling.

Positive predictive value of a single nucleotide polymorphism (SNP)-based NIPT for aneuploidy in twins: Experience from clinical practice

OBJECTIVE

Twins account for approximately 1 in 30 live births in the United States. However, there are limited clinical experience studies published in noninvasive prenatal testing (NIPT) for detecting aneuploidies in twins. This study reports the performance of an SNP-based NIPT in the largest cohort with known outcomes for high-risk aneuploidy results.

METHOD

This is a retrospective analysis of 18,984 results from commercial single-nucleotide polymorphism (SNP)-based NIPT tests performed in twins between October 2, 2017 and December 31, 2019. Follow-up for all 211 high-risk cases was solicited.

RESULTS

Follow-up outcomes were obtained in 105 cases. Positive predictive values (PPVs) for high-risk results were 88.7% (63/71, 95% Confidence Interval [CI]: 79.0%-95.0%) for trisomy 21% and 72.7% (8/11, 95% CI: 39.0%-94.0%) for trisomy 18. The results were stratified into monozygotic (MZ) and dizygotic (DZ). The PPVs in MZ were 100% for both trisomy 21 (4/4, 95% CI: 40%-100%) and trisomy 18 (1/1, 95% CI: 2.5%-100%). No trisomy 13 cases were detected in the MZ group. The PPVs in DZ were 88.1% (59/67, 95% CI: 77.8%-94.7%), 70.0% (7/10, 95% CI: 34.8%-93.3%), and 66.7% (2/3, 95% CI: 9.4%-99.2%) for trisomy 21, trisomy 18, and trisomy 13, respectively.

CONCLUSION

The performance of SNP-based NIPT in this large twin cohort was comparable to previously reported twin NIPT studies. SNP-based NIPT allows for zygosity-based PPV assessment.

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.

Comparing Non-invasive Prenatal Testing With Invasive Testing for the Detection of Trisomy 21

Background Non-invasive prenatal test (NIPT) is an intermediate step between serum screening and invasive diagnostic testing. It involves analysis of the cell-free fetal DNA (cffDNA) present in the maternal blood sample for determining the likelihood of fetal aneuploidy. Owing to its high sensitivity and specificity, NIPT has quickly gained popularity across the globe since its introduction to clinical practice, making it an attractive alternative to the available screening and diagnostic tests in use. Amniocentesis is currently the gold standard test for obtaining fetal DNA and diagnosing fetal trisomy prenatally, but it is invasive and has procedure-related adverse effects. This study aims to compare NIPT and amniocentesis in pregnancies screened positive for fetal trisomy. Material and methods This is an analytic cross-sectional prospective study conducted in the Department of Obstetrics & Gynecology, Patna Medical College and Hospital, for two and half years from December 2018 to June 2021. A total of 34 pregnant women screened positive for trisomy 21, attending the antenatal care outpatient department, in their second trimester, with their written consent, were enrolled in the study. Results Out of 34 pregnant patients, three refused NIPT and directly opted for amniocentesis. A total of 31 pregnant women have undergone NIPT. A total of 28 cases were positive for trisomy 21 on both NIPT and amniocentesis. The sensitivity of NIPT was 100% with the confidence interval being 87.66% to 100.00%. The specificity of NIPT was 100% with the confidence interval being 29.24% to 100.00%. Conclusion The high performance and effectiveness of NIPT are undeniable. Though the process by which this test has to be integrated into the clinical practice needs more study and should be determined with meticulous assessment.

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.

Clinician-reported Chorionicity and Zygosity Assignment using single-nucleotide polymorphism-based cell-free DNA Lessons learned from 55,344 Twin Pregnancies

Objective

Prenatal chorionicity assessment relies on ultrasound, which can be confounded by many factors. Noninvasive assessment of zygosity is possible using single nucleotide polymorphism (SNP)‐based cell‐free DNA testing. Our objective was to determine the relationship between provider‐reported chorionicity and SNP‐cfDNA assignment of twin zygosity.

Methods

All twin pregnancy blood samples received by a reference laboratory between September 27, 2017 and September 8, 2021 were included. Chorionicity assignment was requested on the requisition, recorded as; monochorionic (MC), dichorionic, or “don't know”. SNP‐cfDNA zygosity results, monozygotic (MZ) or dizygotic (DZ), were correlated with chorionicity assignment.

Results

59,471 twin samples (median gestational age = 12.0 weeks at draw) were received and analyzed; 55,344 (93.1%) received zygosity assignment. SNP‐cfDNA reported 16,673 (30.1%) MZ and 38,671 (69.9%) as DZ. Provider‐reported chorionicity was compared to the zygosity assignment for each case. Of 6283 provider‐reported MC twins, 318 (5.1%) were reported as DZ using SNP‐cfDNA.

Conclusion(s)

One in 20 suspected MC twin pregnancies were reported as DZ using SNP‐cfDNA. Approximately 30% of 55,344 twin pregnancies were found to be MZ, including cases where chorionicity was unknown. SNP‐cfDNA zygosity assessment is a useful adjunct assessment for twin pregnancies, particularly those reported as MC or without determined chorionicity.

What's already known about the topic?

The assignment of chorionicity early in pregnancy can improve perinatal outcomes of twin pregnancies. Prenatal assessment of chorionicity relies on ultrasound (US), and the accuracy of US can be confounded by many factors, including gestational age (GA) and operator experience. Noninvasive assessment of zygosity is now possible using single nucleotide polymorphism (SNP)‐based cell‐free DNA (cfDNA).

What does this study add?

This is the first population‐based study describing the correlation between cfDNA assessment of zygosity and chorionicity. In 55,344 twin pregnancies, approximately 30% were found to be monozygotic (MZ), including cases where chorionicity was unknown. We found that one in 20 suspected monochorionic (MC) twin pregnancies were reported as dizygotic (DZ) twins (DZ) by SNP‐cfDNA testing. SNP‐cfDNA zygosity assessment is a useful adjunct assessment for twin pregnancies, particularly those reported as MC or without determined chorionicity.

Systematic evidence-based review: The application of noninvasive prenatal screening using cell-free DNA in general-risk pregnancies

PURPOSE

Noninvasive prenatal screening (NIPS) using cell-free DNA has been assimilated into prenatal care. Prior studies examined clinical validity and technical performance in high-risk populations. This systematic evidence review evaluates NIPS performance in a general-risk population.

METHODS

Medline (PubMed) and Embase were used to identify studies examining detection of Down syndrome (T21), trisomy 18 (T18), trisomy 13 (T13), sex chromosome aneuploidies, rare autosomal trisomies, copy number variants, and maternal conditions, as well as studies assessing the psychological impact of NIPS and the rate of subsequent diagnostic testing. Random-effects meta-analyses were used to calculate pooled estimates of NIPS performance (P < .05). Heterogeneity was investigated through subgroup analyses. Risk of bias was assessed.

RESULTS

A total of 87 studies met inclusion criteria. Diagnostic odds ratios were significant (P < .0001) for T21, T18, and T13 for singleton and twin pregnancies. NIPS was accurate (≥99.78%) in detecting sex chromosome aneuploidies. Performance for rare autosomal trisomies and copy number variants was variable. Use of NIPS reduced diagnostic tests by 31% to 79%. Conclusions regarding psychosocial outcomes could not be drawn owing to lack of data. Identification of maternal conditions was rare.

CONCLUSION

NIPS is a highly accurate screening method for T21, T18, and T13 in both singleton and twin pregnancies.

Monochorionic monoamniotic twin pregnancies

Monoamniotic twin pregnancies are rare, but early diagnosis of such pregnancies is critical, as the incidence of complications in these pregnancies is much higher than in diamniotic or dichorionic twin pregnancies. Overall, only 70% of all monoamniotic twins will survive. Furthermore, approximately half of fetal deaths in these pregnancies are because of the high incidence of fetal anomalies (15%-25%), such as twin reversed arterial perfusion sequence and conjoined twinning. Therefore, early anatomy screening in the first trimester of pregnancy is recommended. Other causes of fetal death in these pregnancies include twin-twin transfusion syndrome, tight cord entanglement, or acute hemodynamic imbalances through the large placental vascular anastomoses. After viability, fetal surveillance can be intensified, as this decreases the risk of in utero death. Both inpatient and outpatient surveillance are reasonable. If otherwise uncomplicated, monoamniotic twins should be delivered at 33 to 34 weeks' gestation. Most centers will deliver by cesarean delivery, but some continue to advocate for vaginal delivery. Lastly, neonatal morbidity is high in monoamniotic twin pregnancies and is mainly related to prematurity.

Calculation of Fetal Fraction for Non-Invasive Prenatal Testing

Estimating the fetal fraction of DNA in a pregnant mother’s blood is a risk-free, non-invasive way of predicting fetal aneuploidy. It is a rapidly developing field of study, offering researchers a plethora of different complementary methods. Such methods include examining the differences in methylation profiles between the fetus and the mother. Others include calculating the average allele frequency based on the difference in genotype of a number of single-nucleotide polymorphisms. Differences in the length distribution of DNA fragments between the mother and the fetus as well as measuring the proportion of DNA reads mapping to the Y chromosome also constitute fetal fraction estimation methods. The advantages and disadvantages of each of these main method types are discussed. Moreover, several well-known fetal fraction estimation methods, such as SeqFF, are described and compared with other methods. These methods are amenable to not only the estimation of fetal fraction but also paternity, cancer, and transplantation monitoring studies. NIPT is safe, and should aneuploidy be detected, this information can help parents prepare mentally and emotionally for the birth of a special needs child.

Performance and Diagnostic Value of Genome-Wide Noninvasive Prenatal Testing in Multiple Gestations

OBJECTIVE

To evaluate the accuracy and diagnostic value of genome-wide noninvasive prenatal testing (NIPT) for the detection of fetal aneuploidies in multiple gestations, with a focus on dichorionic-diamniotic twin pregnancies.

METHODS

We performed a retrospective cohort study including data from pregnant women with a twin or higher-order gestation who underwent genome-wide NIPT at one of the eight Belgian genetic centers between November 1, 2013, and March 1, 2020. Chorionicity and amnionicity were determined by ultrasonography. Follow-up invasive testing was carried out in the event of positive NIPT results. Sensitivity and specificity were calculated for the detection of trisomy 21, 18, and 13 in the dichorionic-diamniotic twin cohort.

RESULTS

Unique NIPT analyses were performed for 4,150 pregnant women with a multiple gestation and an additional 767 with vanishing gestations. The failure rate in multiple gestations excluding vanishing gestations ranged from 0% to 11.7% among the different genetic centers. Overall, the failure rate was 4.8%, which could be reduced to 1.2% after single resampling. There were no common fetal trisomies detected among the 86 monochorionic-monoamniotic and 25 triplet cases. Two monochorionic-diamniotic twins had an NIPT result indicative of a trisomy 21, which was confirmed in both fetuses. Among 2,716 dichorionic-diamniotic twin gestations, a sensitivity of 100% (95% CI 74.12-100%) and a specificity of 100% (95% CI 99.86-100%) was reached for trisomy 21 (n=12). For trisomy 18 (n=3), the respective values were 75% (95% CI 30.06-95.44%) sensitivity and 100% (95% CI 99.86-100%) specificity, and for trisomy 13 (n=2), 100% (95% CI 20.65-100%) sensitivity and 99.96% (95% CI 99.79-99.99%) specificity. In the vanishing gestation group, 28 NIPT results were positive for trisomy 21, 18, or 13, with only five confirmed trisomies.

CONCLUSION

Genome-wide NIPT performed accurately for detection of aneuploidy in dichorionic-diamniotic twin gestations.

Non-invasive prenatal testing in the management of twin pregnancies

Twin pregnancies are common and associated with pregnancy complications and adverse outcomes. Prenatal clinical management is intensive and has been hampered by inferior screening and less acceptable invasive testing. For aneuploidy screening, meta‐analyses show that non‐invasive prenatal testing (NIPT) through analysis of cell‐free DNA (cf‐DNA) is superior to serum and ultrasound‐based tests. The positive predictive value for NIPT is driven strongly by the discriminatory power of the assay and only secondarily by the prior risk. Uncertainties in a priori risks for aneuploidies in twin pregnancies are therefore of lesser importance with NIPT. Additional information on zygosity can be obtained using NIPT. Establishing zygosity can be helpful when chorionicity was not reliably established early in pregnancy or where the there is a concern for one versus two affected fetuses. In dizygotic twin pregnancies, individual fetal fractions can be measured to ensure that both values are satisfactory. Vanishing twins can be identified by NIPT. Although clinical utility of routinely detecting vanishing twins has not yet been demonstrated, there are individual cases where cf‐DNA analysis could be helpful in explaining unusual clinical or laboratory observations. We conclude that cf‐DNA analysis and ultrasound have synergistic roles in the management of multiple gestational pregnancies.

What's already known about this topic?

In singleton pregnancies, non‐invasive prenatal testing (NIPT) for fetal aneuploidy is more effective than conventional serum and ultrasound‐based screening tests.

NIPT is more complex in dizygotic twin pregnancies due to the presence of two fetal genotypes.

Overall fetal fraction is higher in twin pregnancies but the individual contribution for each fetus is lower.

What does this study add?

A review of cell‐free DNA testing in twin pregnancies.

Individual fetal fractions in dizygotic twin pregnancies can be measured.

Zygosity can be established using NIPT and this can be particularly useful when there are concerns about chorionicity or determining whether one versus two fetuses are affected.

Vanishing twins can be detected through NIPT and this testing could be considered for some apparently singleton pregnancies with complications.

Current controversies in prenatal diagnosis: Expanded NIPT that includes conditions other than trisomies 13, 18, and 21 should be offered

Non-invasive prenatal testing (NIPT) based on analysis of cell free DNA circulating in the maternal plasma has been available clinically to screen for chromosomal abnormalities since 2011. There is significant evidence to suggest that NIPT has revolutionised prenatal screening for the common trisomies 13, 18, and 21. However, the evidence in favour of its extended use to screen for conditions other than these trisomies remains a topic of debate with no national or international organisation supporting clinical implementation for these indications. In the debate presented here - "Expanded NIPT that includes conditions other than trisomies 13, 18, and 21 should be offered" - we will see the pros and cons of screening for a wider range of chromosomal problems. The discussion presented swung the vote from 65% in favour and 35% against before the arguments were voiced to 41% in favour and 59% against. This significant swing in the vote indicates that the majority of our community feel more evidence is required before clinical implementation of extended NIPT.

Performance of noninvasive prenatal screening in twin pregnancies: a retrospective study of 5469 twin pregnancies

OBJECTIVES

To evaluate the performance of noninvasive prenatal screening (NIPS) for the fetal common aneuploidy screening in twin pregnancies.

METHODS

The data of 5469 women with twin pregnancies were collected in this retrospective observational study between January 2017 and December 2018. Patients underwent NIPS as first-line screening or after standard serum screening for fetal aneuploidy. The performance of NIPS was examined, and a regression analysis was performed to investigate testing failure in cases of low fetal fraction.

RESULTS

In this study, 2231 (40.8%) patients opted for NIPS as the primary prenatal screening test, and 3238 (59.2%) opted for serum screening, including 440 patients who opted for NIPS after serum screening. Among the 2671 pregnancies with available NIPS outcomes, 11 cases of aneuploidy were identified, seven of trisomy 21 and four of sex chromosome aneuploidy (SCA). The sensitivity and specificity for trisomy 21 were 100% (95% CI, 56.1-100.0%) and 100% (95% CI, 99.8-100.0%), respectively. The positive predictive value (PPV) for SCA was 40.0% (95% CI, 13.7-72.6%). No false negatives were found, with a negative predictive value (NPV) of 100% (95% CI, 99.8-100.0%) in total. In 32 pregnancies who failed NIPS test without available NIPS outcomes due to low fetal fraction, the regression analysis demonstrated that increasing BMI and assisted reproductive technology treatment were significant independent predictors.

CONCLUSIONS

NIPS is a high-performing routine primary prenatal screening test in twin pregnancies, with a high PPV and low false positive rate for detecting trisomy 21. It is also useful to identify common sex chromosome aneuploidies in twin pregnancies, with similar performance to that reported in singleton pregnancy.

Non-Invasive Prenatal Testing: Current Perspectives and Future Challenges

Fetal aneuploidies are among the most common causes of miscarriages, perinatal mortality and neurodevelopmental impairment. During the last 70 years, many efforts have been made in order to improve prenatal diagnosis and prenatal screening of these conditions. Recently, the use of cell-free fetal DNA (cff-DNA) testing has been increasingly used in different countries, representing an opportunity for non-invasive prenatal screening of pregnant women. The aim of this narrative review is to describe the state of the art and the main strengths and limitations of this test for prenatal screening of fetal aneuploidies.