Social and medical need for whole genome high resolution NIPT.

BACKGROUND: Two technological innovations in the last decade significantly influenced the diagnostic yield of prenatal cytogenetic testing: genomic microarray allowing high resolution analysis and noninvasive prenatal testing (NIPT) focusing on aneuploidy. To anticipate future trends in prenatal screening and diagnosis, we evaluated the number of invasive tests in our center and the number of aberrant cases diagnosed in the last decade. METHODS: We retrospectively analyzed fetal chromosomal aberrations diagnosed in 2009-2018 in 8,608 pregnancies without ultrasound anomalies. RESULTS: The introduction of NIPT as the first-tier test led to a substantial decrease in the number of invasive tests and a substantially increased diagnostic yield of aneuploidies in the first trimester. However, we have also noted a decreased detection of submicroscopic aberrations, since the number of invasive tests substantially decreased. We have observed that pregnant women were interested in broader scope of prenatal screening and diagnosis than detection of common trisomies. CONCLUSION: Since the frequency of syndromic disorders caused by microdeletions/microduplications is substantial and current routine NIPT and ultrasound investigations are not able to detect them, we suggest that a noninvasive test with resolution comparable to microarrays should be developed, which will also meet patient's needs.

Placental studies elucidate discrepancies between NIPT showing a structural chromosome aberration and a differently abnormal fetal karyotype.

OBJECTIVE: Placental cytogenetic studies may reveal the origin of discordant noninvasive prenatal testing (NIPT). We performed placental studies to elucidate discordances between NIPT showing a structural chromosome aberration and the fetus having a different chromosome aberration in three cases. METHOD: Diagnostic testing with genomic SNP microarray was performed in three cases with NIPT showing a duplication on 4q (case 1), a terminal deletion of 13q (case 2), and a terminal deletion of 15q (case 3). Placental studies involved SNP array analysis of cytotrophoblast and mesenchymal core of chorionic villi of four placental quadrants. Clinical follow-up was performed as well. RESULTS: Amniotic fluid revealed a different structural chromosome aberration than predicted by NIPT: a terminal 2q deletion (case 1), a segmental uniparental isodisomy of 13q (case 2), and a terminal duplication of 15q and of 13q (case 3). Placental studies revealed the aberration detected with NIPT in the cytotrophoblast, whereas the fetal karyotype was confirmed in the placental mesenchymal core. CONCLUSION: Our study shows that targeted cytogenetic investigations for confirmation of NIPT showing a microscopically visible structural chromosome aberration should be avoided, since another aberration, even a submicroscopic one or one involving another chromosome, may be present in the fetus.