UPD16 itself is not a cause of intrauterine growth restriction

Clinical impacts of genome-wide noninvasive prenatal testing for rare autosomal trisomy

BACKGROUND

Genome-wide noninvasive prenatal testing identifies several rare autosomal trisomies in the general obstetrical population, but its use is questioned by its low positive predictive value. Furthermore, the origin of rare autosomal trisomies and the clinical effect of reporting them has not been sufficiently investigated. In addition, professional societies express their need for data assessing the clinical use of genome-wide noninvasive prenatal testing for rare autosomal trisomies for years.

OBJECTIVE

This study aimed to investigate the origin of rare autosomal trisomies and the clinical effect of disclosing rare autosomal trisomies in clinical settings.

STUDY DESIGN

Women who received noninvasive prenatal testing between March 2021 and March 2022 were prospectively enrolled. Clinical follow-up and cytogenetic and molecular investigations were performed. Posthoc analysis was performed to investigate the association between placental mosaicism and clinical outcomes.

RESULTS

Overall, 154 rare autosomal trisomies were identified in 89,242 pregnancies (0.17%) through noninvasive prenatal testing. In the 120 cases in which cytogenetic and molecular investigations were carried out, the rare autosomal trisomies were found to originate from true fetal mosaicism (n=5), uniparental disomy (n=5), maternal mosaic trisomy (n=3), maternal malignancy (n=1), and confined placental mosaicism (n=106). Clinical follow-up showed that 40% of all rare autosomal trisomy cases had adverse perinatal outcomes. In women with false-positive noninvasive prenatal testing results originating from confined placental mosaicism, the frequency of adverse perinatal outcomes was 26%. More importantly, the placental mosaicism ratio revealed by noninvasive prenatal testing was significantly higher in women who experienced adverse perinatal outcomes than those who did not (0.688 vs 0.332; P<.001).

CONCLUSION

Women with noninvasive prenatal testing results indicative of rare autosomal trisomies are at risk of adverse perinatal outcomes, and that risk can be stratified using chromosomes and the mosaicism ratio revealed by noninvasive prenatal testing. Our data are valuable for obstetrical caregivers advising a patient with a noninvasive prenatal testing result indicative of a rare autosomal trisomy and a false-positive diagnosis and for managing risks during pregnancy.

Confined placental mosaicism and the association with pregnancy outcome and fetal growth: a review of the literature

BACKGROUND

Chromosomal mosaicism can be detected in different stages of early life: in cleavage stage embryos, in blastocysts and biopsied cells from blastocysts during preimplantation genetic testing for aneuploidies (PGT-A) and later during prenatal testing, as well as after birth in cord blood. Mosaicism at all different stages can be associated with adverse pregnancy outcomes. There is an onward discussion about whether blastocysts diagnosed as chromosomally mosaic by PGT-A should be considered safe for transfer. An accurate diagnosis of mosaicism remains technically challenging and the fate of abnormal cells within an embryo remains largely unknown. However, if aneuploid cells persist in the extraembryonic tissues, they can give rise to confined placental mosaicism (CPM). Non-invasive prenatal testing (NIPT) uses cell-free (cf) DNA released from the placenta in maternal blood, facilitating the detection of CPM. In literature, conflicting evidence is found about whether CPM is associated with fetal growth restriction (FGR) and/or other pregnancy outcomes. This makes counselling for patients by clinicians challenging and more knowledge is needed for clinical decision and policy making.

OBJECTIVE AND RATIONALE

The objective of this review is to evaluate the association between CPM and prenatal growth and adverse pregnancy outcomes. All relevant literature has been reviewed in order to achieve an overview on merged results exploring the relation between CPM and FGR and other adverse pregnancy outcomes.

SEARCH METHODS

The following Medical Subject Headings (MESH) terms and all their synonyms were used: placental, trophoblast, cytotrophoblast, mosaicism, trisomy, fetal growth, birth weight, small for gestational age and fetal development. A search in Embase, PubMed, Medline Ovid, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL) and Google Scholar databases was conducted. Relevant articles published until 16 July 2020 were critically analyzed and discussed.

OUTCOMES

There were 823 articles found and screened based on their title/abstract. From these, 213 articles were selected and full text versions were obtained for a second selection, after which 70 publications were included and 328 cases (fetuses) were analyzed. For CPM in eight different chromosomes (of the total 14 analyzed), there was sufficient evidence that birth weight was often below the 5th percentile of fetal growth standards. FGR was reported in 71.7% of CPM cases and preterm birth (<37 weeks of delivery) was reported in 31.0% of cases. A high rate of structural fetal anomalies, 24.2%, in cases with CPM was also identified. High levels of mosaicism in CVS and presence of uniparental disomy (UPD) were significantly associated with adverse pregnancy outcomes.

WIDER IMPLICATIONS

Based on the literature, the advice to clinicians is to monitor fetal growth intensively from first trimester onwards in case of CPM, especially when chromosome 2, 3, 7, 13, 15, 16 and 22 are involved. In addition to this, it is advised to examine the fetuses thoroughly for structural fetal anomalies and raise awareness of a higher chance of (possibly extreme) premature birth. Despite prematurity in nearly a fifth of cases, the long-term follow-up of CPM life borns seems to be positive. More understanding of the biological mechanisms behind CPM will help in prioritizing embryos for transfer after the detection of mosaicism in embryos through PGT-A.

Performance of Chromosomal Microarray Analysis for Detection of Copy Number Variations in Fetal Echogenic Bowel

BACKGROUND

Fetal echogenic bowel (FEB) is associated with an increased risk of poor pregnant outcomes; however, karyotyping fails to detect copy number variations (CNVs) in FEB. This study aimed to evaluate the performance of chromosomal microarray analysis (CMA) for detection of FEB.

METHODS

The medical records of 147 pregnant women with FEB recruited during December 2015 to December 2018 were retrospectively reviewed, and prenatal samples were collected for karyotyping and CMA. The detection of chromosomal abnormality was compared between karyotyping and CMA.

RESULTS

Karyotyping identified eight cases with abnormal karyotypes (5.44% prevalence), including four fetuses with pathogenic aneuploidy, three with chromosome polymorphism and one with balanced chromosome translocation. CMA identified 13 abnormal CNVs (8.84% prevalence), including 4 fetuses with pathogenic aneuploidy as detected by karyotyping and 9 additional CNVs with normal karyotypes; however, CMA failed to detect chromosome polymorphism and balanced chromosome translocation. In fetuses with isolated FEB, no cases presented pathogenic findings and CMA detected two cases with variants of uncertain significance (VOUS). In cases presenting FEB along with other ultrasound abnormalities, CMA detected three cases with pathogenic CNVs and four cases with VOUS in addition to four cases with aneuploidy. There was no significant difference in the detection of abnormal CNVs between the fetuses with echogenic bowel alone and along with other ultrasound abnormalities (10% vs 8.67%, P > 0.05). Except 9 fetuses lost to the follow-up, the other 138 fetuses with echogenic bowel were successfully followed up. Pregnancy was terminated in 5 fetuses with chromosomal abnormality, 2 with pathogenic CNVs and 1 with VOUS, and other 16 with normal karyotypes and CMA findings but showing ultrasound abnormalities or multiple malformations.

CONCLUSION

Isolated FEB is associated with a good prognosis, and a satisfactory pregnant outcome is expected for fetuses with echogenic bowel that are negative for chromosomal anomalies and other severe structure abnormalities. CMA shows an important value in the genetic diagnosis of FEB. As a supplement to karyotyping, CMA may improve the accuracy of prenatal diagnosis of fetal intestinal malformations in pregnant women with FEB.