Estimation of Detection Rates of Aneuploidy in High-Risk Pregnancy Using an Approach Based on Nuchal Translucency and Non-Invasive Prenatal Testing: A Cohort Study

Different Cutoff Values for Increased Nuchal Translucency in First-Trimester Screening to Predict Fetal Chromosomal Abnormalities

INTRODUCTION

Increased nuchal translucency (NT) is closely related to an increased risk of chromosomal abnormalities. However, the criterion of increased NT for invasive prenatal diagnosis remains controversial, as the cutoff values are inconsistent among countries. This study was conducted to compare the various cutoff values of increased NT and calculate the incidence of chromosomal abnormalities to determine the predictive ability of these cutoff values in conventional chromosome analysis.

METHODS

A total of 3223 invasive samples with increased nuchal translucency (NT) or other non-ultrasound indications were collected from singleton pregnant women. Samples with isolated increased NT were divided into five groups based on the NT thickness: 909 samples in the NT ≥2.5 mm group, 819 samples in the NT ≥95th group, 547 samples in the NT ≥99th group, 527 samples in the NT ≥3.0 mm group, and 253 samples in the NT ≥3.5 mm group; 2301 samples with normal NT were considered as the control group. All five groups were karyotyped and the results were compared. The accuracy of the NT cutoff value for the screening of chromosomal abnormalities was assessed using receiver operating characteristic curve analysis.

RESULTS

Detection of all chromosomal aberrations and trisomy 21 showed that the sensitivity and false-positive rate decreased sequentially in the NT ≥2.5 mm, NT ≥95th, NT ≥3 mm, NT ≥99th, and NT ≥3.5 mm groups, whereas the specificity, positive predictive value, and false-negative rates increased sequentially. Comprehensive analysis of various factors, including sensitivity and specificity, revealed values equal to or higher than the calculated 95th percentile of NT distribution, which showed a sensitivity of 49.2% and specificity of 75.67% for detecting all aneuploidies and a sensitivity of 64% and specificity of 75.45% for trisomy 21, exhibiting the highest ability for the screening of chromosomal defects in first-trimester screening.

CONCLUSION

For different thresholds of NT thickness, values equal to or higher than the calculated 95th percentile of the NT distribution showed the highest ability for the screening of chromosomal defects in first-trimester screening.

Audit of the first > 7500 noninvasive prenatal aneuploidy tests in a Swiss genetics center

Objectives

Noninvasive prenatal testing (NIPT) is actually the most accurate method of screening for fetal chromosomal aberration (FCA). We used pregnancy outcome record to evaluate a complete data set of single nucleotide polymorphism-based test results performed by a Swiss genetics center.

Materials and methods

The Panorama^® test assesses the risk of fetal trisomies (21, 18 and 13), gonosomal aneuploidy (GAN), triploidy or vanishing twins (VTT) and five different microdeletions (MD). We evaluated all 7549 test results meeting legal and quality requirements taken in women with nondonor singleton pregnancies between April 2013 and September 2016 classifying them as high or low risk. Follow-up ended after 9 months, data collection 7 months later.

Results

The Panorama^® test provided conclusive results in 96.1% of cases, detecting 153 FCA: T21 n = 76, T18 n = 19, T13 n = 15, GAN n = 19, VTT n = 13 and MD n = 11 (overall prevalence 2.0%). Pregnancy outcome record was available for 68.6% of conclusive laboratory results, including 2.0% high-risk cases. In this cohort the Panorama^® test exhibited 99.90% sensitivity for each trisomy; specificity was 99.90% for T21, 99.98% for T18 and 99.94% for T13. False positive rate was 0.10% for T21, 0.02% for T18 and 0.06% for T13.

Conclusion

SNP-based testing by a Swiss genetics center confirms the expected accuracy of NIPT in FCA detection.

Fetal Cystic Hygroma Associated with Terminal 2p25.1 Duplication and Terminal 3p25.3 Deletion: Cytogenetic, Fluorescent in Situ Hybridization and Microarray Familial Characterization of Two Different Chromosomal Structural Rearrangements

We report a prenatally diagnosed case of partial trisomy 2p and partial monosomy 3p, resulting from unbalanced translocation (2;3)(p25.1;p25.3) of paternal origin. Parents were non consanguineous Caucasians, with familial history of recurrent miscarriages on the father’s side. Detailed sonographic examination of the fetus showed a septated cystic hygroma measuring 6 mm at 13 weeks’ gestation. Karyotyping and fluorescent in situ hybridization (FISH) analysis of cultured amniotic fluid cells revealed an unbalanced translocation der(3)t(2;3)(p25.1; p25.3) and apparently balanced inv(3)(p13p25.3) in a fetus. Parental cytogenetic evaluation using karyotyping and FISH analysis showed the presence of both a balanced translocation and a paracentric inversion in father t(2;3) (p25.1;p25.3) inv(3)(p13p25.3). Microarray analysis showed a 11.6 Mb deletion at 3p26.3-p25.3 and duplication of 10.5 Mb at the 2p25.3-p25 region. The duplicated region at 2p25.1p25.3 contains 45 different genes, where 12 are reported as OMIM morbid genes with different phenotypical implications. The deleted region at 3p26.3-p25.3 contains 65 genes, out of which 27 are OMIM genes.

Three of these (CNTN4, SETD5 and VHL) were curated by Clingene Dosage Gene Map and were given a high haplo-insufficiency score. Genes affected by the unbalanced translocation could have contributed to some specific phenotypic changes of the fetus in late pregnancy. The application of different cytogenetic methods was essential in our case, allowing the detection of different types of structural chromosomal aberrations and more thorough genetic counseling for future pregnancies.

Nuchal translucency of 3.0-3.4 mm an indication for NIPT or microarray? Cohort analysis and literature review

Introduction

Currently fetal nuchal translucency (NT) ≥3.5 mm is an indication for invasive testing often followed by chromosomal microarray. The aim of this study was to assess the risks for chromosomal aberrations in fetuses with an NT 3.0‐3.4 mm, to determine whether invasive prenatal testing would be relevant in these cases and to assess the residual risks in fetuses with normal non‐invasive prenatal test (NIPT) results.

Material and methods

A retrospective study and meta‐analysis of literature cases with NT between 3.0 and 3.4 mm and 2 cohorts of pregnant women referred for invasive testing and chromosomal microarray was performed: Rotterdam region (with a risk >1:200 and NT between 3.0 and 3.4 mm) tested in the period July 2012 to June 2019 and Central Denmark region (with a risk >1:300 and NT between 3.0 and 3.4 mm) tested between September 2015 and December 2018.

Results

A total of 522 fetuses were referred for invasive testing and chromosomal microarray. Meta‐analysis indicated that in 1:7.4 (13.5% [95% CI 8.2%‐21.5%]) fetuses a chromosomal aberration was diagnosed. Of these aberrant cases, 47/68 (69%) involved trisomy 21, 18, and 13 and would potentially be detected by all NIPT approaches. The residual risk for missing a (sub)microscopic chromosome aberration depends on the NIPT approach and is highest if NIPT was performed only for common trisomies–1:21 (4.8% [95% CI 3.2%‐7.3%]). However, it may be substantially lowered if a genome‐wide 10‐Mb resolution NIPT test was offered (~1:464).

Conclusions

Based on these data, we suggest that the NT cut‐off for invasive testing could be 3.0 mm (instead of 3.5 mm) because of the high risk of 1:7.4 for a chromosomal aberration. If women were offered NIPT first, there would be a significant diagnostic delay because all abnormal NIPT results need to be confirmed by diagnostic testing. If the woman had already received a normal NIPT result, the residual risk of 1:21 to 1:464 for chromosome aberrations other than common trisomies, dependent on the NIPT approach, should be raised. If a pregnant woman declines invasive testing, but still wants a test with a broader coverage of clinically significant conditions then the genome‐wide >10‐Mb resolution NIPT test, which detects most aberrations, could be proposed.

Non-invasive prenatal testing (NIPT): Europe's first multicenter post-market clinical follow-up study validating the quality in clinical routine

PURPOSE

Non-invasive prenatal tests (NIPT) for the determination of fetal aneuploidies from maternal blood are firmly established in clinical routine. For the first time, the accuracy of an NIPT for the determination of trisomies 21, 18 and 13 in singleton pregnancies was assessed by means of a prospective German-wide multicenter post-market clinical follow-up study, to reliably evaluate the quality in clinical routine.

METHODS

The study covered the indications for testing, the test results, the rate of invasive diagnostics and the pregnancy outcome. 2232 cases were tested for trisomy 21. Of these, 1946 cases were additionally examined for trisomy 18 and 13.

RESULTS

Sensitivity and specificity for trisomy 21 (43/43) and for trisomy 13 (2/2) were 100%, for trisomy 18 the sensitivity was 80% (4/5) with a specificity of 99.8%. Three false-positive results for trisomy 18 were observed (FPR 0.15%). The no-call rate was 0.5%. In this subgroup, 27.3% (3/11) aneuploidies were diagnosed. The rate of invasive procedures was 2.6%.

CONCLUSION

NIPT provides a very high quality for the fetal trisomies 21, 13 and 18 in clinical routine. The results support the recommendation that NIPT should be offered after genetic counseling and only in conjunction with a qualified ultrasound examination.

The role of ultrasound in women who undergo cell-free DNA screening

The introduction of cell-free DNA screening for aneuploidy into obstetric practice in 2011 revolutionized the strategies utilized for prenatal testing. The purpose of this document is to review the current data on the role of ultrasound in women who have undergone or are considering cell-free DNA screening. The following are Society for Maternal-Fetal Medicine recommendations: (1) in women who have already received a negative cell-free DNA screening screen, ultrasound at 11-14 weeks of gestation solely for the purpose of nuchal translucency measurement (Current Procedural Terminology code 76813) is not recommended (grade 1B); (2) we recommend that diagnostic testing should not be recommended to patients solely for the indication of an isolated soft marker in the setting of a negative cell-free DNA screen (grade 2B); (3) in women with an isolated soft marker without other clinical implications (ie, choroid plexus cyst or echogenic intracardiac focus) and a negative cell-free DNA screen, we recommend describing the finding as not clinically significant or as a normal variant (grade 2B); (4) in women with an isolated soft marker that has no other clinical implication (ie, choroid plexus cyst or echogenic intracardiac focus) and a negative first- or second-trimester screening result, we recommend describing the finding as not clinically significant or as a normal variant (grade 2B); (5) we recommend that all women in whom a structural abnormality is identified by ultrasound should be offered diagnostic testing with chromosomal microarray (grade 1A); and (6) we recommend against routine screening for microdeletions with cell-free DNA screening (grade 1B).

Chromosomal abnormalities not currently detected by cell-free fetal DNA: a retrospective analysis at a single center

BACKGROUND

Cell-free fetal DNA analysis is used as a screening test to identify pregnancies that are at risk for common autosomal and sex chromosome aneuploidies.

OBJECTIVE

The purpose of this study was to investigate the chromosomal abnormalities that would not be detected by cell-free fetal DNA in a single medical center.

STUDY DESIGN

This was a retrospective cohort analysis of 3182 consecutive invasive diagnostic procedures that were performed at Montefiore Medical Center's Division of Reproductive and Medical Genetics from January 1, 2009 to August 31, 2014. All patients underwent cytogenetic analysis; one-third of the patients (1037/3182) went through chromosomal microarray analysis.

RESULTS

Clinically significant chromosomal abnormalities were detected in 220 of 3140 cases (7%) after we excluded multiple gestation pregnancies (n = 42). Of these 125 cases (57%) were diagnosed with the common autosomal trisomies that involved chromosomes 21, 18, and 13 and with sex chromosome aneuploidies. There were 23 mosaic karyotypes; 8 of them involved trisomy in chromosomes 21 and 13; 5 of them were sex chromosome mosaics, and 10 of them were other mosaic cases. Five cases of triploidy were detected. Additionally, 19 unbalanced chromosomal rearrangements, a rare autosomal trisomy, and 47 clinically significant findings on chromosomal microarray analysis were diagnosed. Based on the published detection rates of cell-free fetal DNA testing and considering the "no-results" rate, we calculated that 99 of 220 chromosomal changes (45%) could not have been detected by cell-free fetal DNA testing: 16 of the 125 common aneuploidies and sex chromosome aneuploidies, 1 of the 5 triploidy cases, 15 of the 23 mosaic cases, all cases of unbalanced chromosomal rearrangements (n = 19), rare autosomal trisomy (n = 1), and 47 clinically significant chromosomal microarray abnormalities.

CONCLUSIONS

Current cell-free DNA testing could not detect up to one-half of the clinically significant chromosomal abnormalities that were found, which included clinically significant chromosomal microarray abnormalities. Among the 99 abnormal karyotypes that were not identified by cell-free DNA screening, 79% were from women with abnormal screening or abnormal ultrasound finding; 21% were from women who underwent invasive testing simply for advanced maternal age/concern, with no other risk factors or ultrasound findings. This information highlights the limitations of cell-free DNA screening and the importance of counseling patients about all prenatal screening and diagnostic procedures and about the added gain of invasive testing with karyotype and microarray.