[Value of non-invasive prenatal testing for rare autosomal trisomies in fetuses]

OBJECTIVE

To evaluate the value of non-invasive prenatal testing(NIPT)for detecting rare autosomal trisomies in fetuses.

METHODS

We retrospectively analyzed the data of cases with rare autosomal trisomies detected by NIPT in our hospital from January, 2019 to April, 2023.Invasive prenatal diagnostic tests including chromosome karyotype analysis, chromosome microarray analysis, copy number variation sequencing, and fluorescence in situ hybridization were performed in all the cases after clinical counseling, and their test results and pregnancy outcomes were analyzed.

RESULTS

Among 25 282 women receiving NIPT, 56(0.22%)were found to have high risks for rare autosomal trisomies in circulating plasma DNA.Trisomy 7 was the most frequently detected trisomy, accounting for 45% of the total cases(25/56), while trisomies 1, 4, 17, and 19 were not detected.Among the 46 cases with genetic results of the fetuses, 10 were identified to have true fetal mosaicism.The overall positive predictive value of NIPT was 22%(10/46)for rare autosomal trisomies, and 10% for trisomy 7(2/20).Of the 52 cases followed up for pregnancy outcomes, 33(63%)cases without fetal mosaicism resulted in normal live births, while 10 had unfavorable outcomes including fetal growth restriction, preterm birth, and maternal complications, and among them fetal growth restriction was the most typical and the earliest condition observed in these cases.Among the 22 followed up cases of non-true mosaicism for trisomy 7, 82% resulted in normal live births.

CONCLUSION

NIPT increases the detection rate of true fetal mosaicism but with a low positive predictive value.Most of the cases with non-true mosaicism, particularly trisomy 7, can have favorable outcomes.NIPT can also be useful in identifying causes of fetal growth restriction in the second and third trimesters when invasive prenatal testing does not reveal abnormalities.

Clinical impact of additional findings detected by genome-wide non-invasive prenatal testing: Follow-up results of the TRIDENT-2 study

In the TRIDENT-2 study, all pregnant women in the Netherlands are offered genome-wide non-invasive prenatal testing (GW-NIPT) with a choice of receiving either full screening or screening solely for common trisomies. Previous data showed that GW-NIPT can reliably detect common trisomies in the general obstetric population and that this test can also detect other chromosomal abnormalities (additional findings). However, evidence regarding the clinical impact of screening for additional findings is lacking. Therefore, we present follow-up results of the TRIDENT-2 study to determine this clinical impact based on the laboratory and perinatal outcomes of cases with additional findings. Between April 2017 and April 2019, additional findings were detected in 402/110,739 pregnancies (0.36%). For 358 cases, the origin was proven to be either fetal (n = 79; 22.1%), (assumed) confined placental mosaicism (CPM) (n = 189; 52.8%), or maternal (n = 90; 25.1%). For the remaining 44 (10.9%), the origin of the aberration could not be determined. Most fetal chromosomal aberrations were pathogenic and associated with severe clinical phenotypes (61/79; 77.2%). For CPM cases, occurrence of pre-eclampsia (8.5% [16/189] vs 0.5% [754/159,924]; RR 18.5), and birth weight <2.3rd percentile (13.6% [24/177] vs 2.5% [3,892/155,491]; RR 5.5) were significantly increased compared to the general obstetric population. Of the 90 maternal findings, 12 (13.3%) were malignancies and 32 (35.6%) (mosaic) pathogenic copy number variants, mostly associated with mild or no clinical phenotypes. Data from this large cohort study provide crucial information for deciding if and how to implement GW-NIPT in screening programs. Additionally, these data can inform the challenging interpretation, counseling, and follow-up of additional findings.

Pregnancy outcomes of rare autosomal trisomies results in non-invasive prenatal screening: clinical follow-up data from a single tertiary centre

This study was performed to assess the association between detection of rare autosomal trisomies (RATs) by non-invasive prenatal screening (NIPS) and adverse pregnancy outcomes. We retrospectively analyzed women with high-risk RATs results from January 2014 to December 2020. The women's clinical information was collected, and their pregnancy outcomes were compared with those of women with low-risk results. In total, 151 (0.24%) RATs results were reported among 62,752 NIPS examinations. Sixty-five women chose to undergo amniocentesis for confirmation, which revealed 3 cases of true fetal mosaicism for RATs and a positive predictive value of 4.6% (3/65). Among the 139 women with available outcomes, 26 (18.7%) had a preterm birth, 10 (7.2%) underwent pregnancy termination because of fetal defects and 5 (3.6%) had miscarriages. Interestingly, compared with the control group, pregnancies in which NIPS revealed trisomy 16 (T16), T22, T9 and T2 were at higher risk of adverse outcomes, including preterm birth, miscarriage and ultrasound abnormalities. However, the risk of adverse outcomes was comparable between the control group and pregnancies with positive results of T7, T3, T8 and T20. In summary, the risk of adverse pregnancy outcomes was higher in women with specific RATs-positive NIPS results. Pregnancies with T16, T22, T9 and T2 results, even if false-positive, should be considered high-risk pregnancies.

The Clinical Utility of Non-invasive Prenatal Testing for Pregnant Women With Different Diagnostic Indications

Background

Our aim was to evaluate the clinical utility of non-invasive prenatal testing for pregnant women with different diagnostic indications.

Methods

In eight counties and districts of Yancheng, we studied 13,149 pregnant women with different indications who were offered NIPT for fetal screening, including for sex chromosomal aneuploidies (SCAs), rare autosomal trisomies (RATs), and subchromosomal copy number variations (CNVs). The purpose was to compare the detection of positive predictive values (PPVs) of different indications with the use of NIPT. The results were validated by karyotyping, chromosomal microarray analysis (CMA), or follow-up of pregnancy outcomes.

Results

13,149 maternal plasma samples were sequenced, among which 28 samples (0.2%) failed the sequencing quality control. The remaining 13,121 samples were analyzed, and birth follow-up missed 2,192 samples (16.7%). The PPVs of NIPT results for trisomy 21 (T21) and trisomy 18 (T18) and SCAs were 96.67, 63.64, and 31.34%, respectively. Among the advanced maternal age (AMA), serum screening high risk (SSHR), serum screening intermediate risk (SSIR), and voluntary screening (VS) groups, the PPVs for the common trisomies were 81.25, 85.71, 100, and 70%, respectively; the PPVs for total chromosomal abnormalities were 55.82, 65.22, 23.08, and 36.59%, respectively.

Conclusion

NIPT for T21 and T18 and SCAs screening were ideal, and the PPVs for trisomy 13 (T13), RATs, and CNVs were low. For the AMA and VS groups, NIPT could be used as a first-line screening program; for SSHR and SSIR groups, NIPT could be used as a second-line supplementary screening program.

TRIDENT-2: National Implementation of Genome-wide Non-invasive Prenatal Testing as a First-Tier Screening Test in the Netherlands

The Netherlands launched a nationwide implementation study on non-invasive prenatal testing (NIPT) as a first-tier test offered to all pregnant women. This started on April 1, 2017 as the TRIDENT-2 study, licensed by the Dutch Ministry of Health. In the first year, NIPT was performed in 73,239 pregnancies (42% of all pregnancies), 7,239 (4%) chose first-trimester combined testing, and 54% did not participate. The number of trisomies 21 (239, 0.33%), 18 (49, 0.07%), and 13 (55, 0.08%) found in this study is comparable to earlier studies, but the Positive Predictive Values (PPV)-96% for trisomy 21, 98% for trisomy 18, and 53% for trisomy 13-were higher than expected. Findings other than trisomy 21, 18, or 13 were reported on request of the pregnant women; 78% of women chose to have these reported. The number of additional findings was 207 (0.36%); these included other trisomies (101, 0.18%, PPV 6%, many of the remaining 94% of cases are likely confined placental mosaics and possibly clinically significant), structural chromosomal aberrations (95, 0.16%, PPV 32%,) and complex abnormal profiles indicative of maternal malignancies (11, 0.02%, PPV 64%). The implementation of genome-wide NIPT is under debate because the benefits of detecting other fetal chromosomal aberrations must be balanced against the risks of discordant positives, parental anxiety, and a potential increase in (invasive) diagnostic procedures. Our first-year data, including clinical data and laboratory follow-up data, will fuel this debate. Furthermore, we describe how NIPT can successfully be embedded into a national screening program with a single chain for prenatal care including counseling, testing, and follow-up.

Cell-free DNA analysis in maternal blood: comparing genome-wide versus targeted approach as a first-line screening test

Objectives: To evaluate the failure rate and performance of cell-free DNA (cfDNA) testing as a first-line screening method for major trisomies, performed by two laboratories using different analytical methods: a targeted chromosome-selective method (Harmony^® prenatal Test) versus a home-brew genome-wide (GW) massively parallel sequencing method (HB-cfDNA test), and to evaluate the clinical value of incidental findings for the latter method.Methods: CfDNA testing was performed in 3137 pregnancies with the Harmony^® prenatal Test and in 3373 pregnancies with the HB-cfDNA test. Propensity score analysis was used to match women between both groups for maternal age, weight, gestational age at testing, in vitro fertilization, rate of twin pregnancies and that of aneuploidies. Detection rates for trisomy 21 were compared between the 2 laboratories. For the HB-cfDNA test, cases with rare incidental findings were reported, including their clinical follow-up.Results: The Harmony^® prenatal Test failed at the first attempt in 90 (2.9%) of 3114 women and the HB-cfDNA test in 413 (12.2%) of 3373 women. Postmatched comparisons of the women's characteristics indicate a significantly lower failure rate in the Harmony^® group (2.8%) than in the HB cfDNA group (12.4%; p < .001). Of the 90 women in whom the Harmony^® prenatal Test failed, 61 had a repeat test, which still failed in 10, and of the 413 women in whom the HB-cfDNA test failed, 379 had a repeat test, which still failed in 110. The total failure rate after one or two attempts was therefore 1.3% (39/3114) for Harmony^® and 4.3% (144/3373) for the HB cfDNA test. After the first or second Harmony^® prenatal Test, a high-risk result was noted in 17 of the 17 cases with trisomy 21, in 5 of the seven cases with trisomy 18, and a no-call in two cases, and in the one case with trisomy 13. The respective numbers for the HB-cfDNA test are 17 of the 18 cases with trisomy 21, and a no-call in one case, 2 of the two cases with trisomy 18, and in 2 of the three cases with trisomy 13, and a no-call in one. Of the 3373 women with the HB-cfDNA test, a rare incidental finding was noted in 28 (0.8%) of the cases, of which only 2 were confirmed on amniocytes (one with microduplication 1q21.1q21.2 and one with a deletion Xp21.1), and in another case a deletion rather than a duplication of the long arm of chromosome 8 was found. In all 28 cases, there was normal clinical follow-up.Conclusions: Comparison of cfDNA testing between these two laboratories showed a four-fold lower failure rate with the Harmony^® prenatal Test, with a similar detection rate for trisomy 21. We showed no clinical relevance of disclosing additional findings beyond common trisomies with the GW HB-cfDNA test.

Outcomes in pregnancies with a confined placental mosaicism and implications for prenatal screening using cell-free DNA

PURPOSE

To assess the association between confined placental mosaicism (CPM) and adverse pregnancy outcome.

METHODS

A retrospective cohort study was carried out evaluating the outcome of pregnancies with and without CPM involving a rare autosomal trisomy (RAT) or tetraploidy. Birthweight, gestational age at delivery, fetal growth restriction (FGR), Apgar score, neonatal intensive care admission, preterm delivery, and hypertensive disorders of pregnancy were considered.

RESULTS

Overall 181 pregnancies with CPM and 757 controls were recruited. Outcome information was available for 69% of cases (n = 124) and 62% of controls (n = 468). CPM involving trisomy 16 (T16) was associated with increased incidence of birthweight <3rd centile (P = 0.007, odds ratio [OR] = 11.2, 95% confidence interval [CI] = 2.7-47.1) and preterm delivery (P = 0.029, OR = 10.2, 95% CI = 1.9-54.7). For the other RATs, an association with prenatally diagnosed FGR was not supported by birthweight data and there were no other strong associations with adverse outcomes.

CONCLUSION

Excluding T16, the incidence of adverse pregnancy outcomes for pregnancies carrying a CPM is low. RATs can also be identified through genome-wide cell-free DNA screening. Because most of these will be attributable to CPMs, we conclude that this screening is of minimal benefit.

Expanding the indications for cell-free DNA in the maternal circulation: clinical considerations and implications

Noninvasive prenatal testing for fetal aneuploidy using cell-free DNA has been widely integrated into routine obstetrical care. The scope of cell-free DNA testing has expanded from trisomies 21, 18, and 13 to include sex chromosome conditions, panels of specific microdeletions, and more recently genome-wide copy number variants and rare autosomal trisomies. Because the technical ability to test for a condition does not necessarily correspond with a clinical benefit to a population or to individual pregnant women, the benefits and harms of screening programs must be carefully weighed before implementation. Application of the World Health Organization criteria to cell-free DNA screening is informative when considering implementation of expanded cell-free DNA test menus. Most microdeletions and duplications are rare to the point that the prevalence has not even been defined and their natural history cannot be reliably predicted in the prenatal period. At the current time, scientific evidence regarding clinical performance of expanded cell-free DNA panels is lacking. Expanded cell-free DNA menus therefore create a dilemma for diagnosis, treatment, and counseling of patients. The clinical utility of expanding cell-free DNA testing to include panels of microdeletions and genome-wide assessment of large chromosomal imbalances has yet to be demonstrated; as such, the clinical implementation of this testing is premature.