Discrepancy between Non-invasive Prenatal Genetic Testing (NIPT) and Amniotic Chromosomal Test due to Placental Mosaicism: A Case Report and Literature Review

Positive predictive value of noninvasive prenatal testing for sex chromosome abnormalities

BACKGROUND

Early and intermediate serological screening cannot detect sex chromosome abnormalities. Currently, noninvasive prenatal testing (NIPT) is the only procedure available for screening such disorders; however, its use is controversial.

METHODS AND RESULTS

A total of 47,855 pregnant women underwent NIPT at our referral center from January 2014 to December 2020. Of the 314 patients with a positive NIPT indicating sex chromosome abnormalities, 260 were screened via karyotype analysis and single nucleotide polymorphism (SNP) array after amniotic fluid extraction; 96 cases were confirmed. Karyotype analysis and SNP array were consistent in the diagnosis of 88 out of the 96 fetuses. The positive predictive value (PPV) for sex chromosome abnormalities was found to be 36.9%. The PPV in patients aged 30-34 years was significantly higher than that in patients aged < 30 years. No statistically significant difference was observed on the PPV among patients with or without previous adverse pregnancy outcomes. Moreover, 83 women carrying fetuses were diagnosed with a sex chromosome abnormality terminated their pregnancy.

CONCLUSIONS

Improvements in detection and analytical technologies are needed to increase the accuracy of sex chromosome abnormalities detection. Pregnant women with a positive NIPT for these abnormalities may require invasive diagnostic procedures such as karyotype analysis and SNP array for better genetic counseling.

Discrepancy between non-invasive prenatal testing result and fetal karyotype caused by rare confined placental mosaicism: A case report

BACKGROUND

Confined placental mosaicism (CPM) is one of the major reasons for discrepancies between the results of non-invasive prenatal testing (NIPT) and fetal karyotype analysis.

CASE SUMMARY

We encountered a primiparous singleton pregnant woman with a rare CPM consisting of 47,XY,+21; 47,XXY; and 46,XY, who obtained a false-positive result on NIPT with a high risk for trisomy 21. Copy-number variation sequencing on amniotic fluid cells, fetal tissue, and placental biopsies showed that the fetal karyotype was 47,XXY, while the placenta was a rare mosaic of 47,XY,+21; 47,XXY; and 46,XY.

CONCLUSION

The patient had a rare CPM consisting of 47,XY,+21; 47,XXY; and 46,XY, which caused a discrepancy between the result of NIPT and the actual fetal karyotype. It is important to remember that NIPT is a screening test, not a diagnostic test. Any positive result should be confirmed with invasive testing, and routine ultrasound examination is still necessary after a negative result.

Genetic Background of Fetal Growth Restriction

Fetal growth restriction (FGR) is one of the most formidable challenges in present-day antenatal care. Pathological fetal growth is a well-known factor of not only in utero demise in the third trimester, but also postnatal morbidity and unfavorable developmental outcomes, including long-term sequalae such as metabolic diseases, diabetic mellitus or hypertension. In this review, the authors present the current state of knowledge about the genetic disturbances responsible for FGR diagnosis, divided into fetal, placental and maternal causes (including preeclampsia), as well as their impact on prenatal diagnostics, with particular attention on chromosomal microarray (CMA) and noninvasive prenatal testing technique (NIPT).

Efficiency of Noninvasive Prenatal Testing for Sex Chromosome Aneuploidies

OBJECTIVE

This study was designed to investigate the efficiency of noninvasive prenatal testing (NIPT) for screening fetal sex chromosome aneuploidies (SCAs) through sequencing of cell-free DNA in maternal plasma.

METHODS

This is a retrospective study on the positive NIPT results for SCAs collected from our hospital between January 2012 and December 2018. Samples with positive NIPT results for SCAs were then confirmed by prenatal or postnatal karyotyping analysis.

RESULTS

After cytogenetic analysis, abnormal karyotypes were confirmed in 104 cases and the overall positive predictive value (PPV) of NIPT for SCAs was 43.40% (102/235). The most frequently detected karyotypes included 47,XXY (n = 42), 47,XXX (n = 20), 47,XYY (n = 16), and 45,X (n = 2). Meanwhile, 10 cases were confirmed with mosaic karyotype 45,X/46,XX and 14 cases with numerical or structural chromosome abnormalities, including a double trisomy 48,XXX,+18. Cytogenetic results from the other 131 cases showed normal XX or XY, which were discordant with NIPT results. Upon analysis of parental karyotypes, 29 (12.34%) showed false positivity in NIPT results that were caused by maternal sex chromosome abnormalities.

CONCLUSION

NIPT is an effective screening tool for SCA with a PPV of 43.40%. Maternal karyotype abnormalities occurred in 12.34% of the cases with abnormal NIPT. Diagnostic testing of the fetus and the mother are recommended.

A placental trisomy 2 detected by NIPT evolved in a fetal small Supernumerary Marker Chromosome (sSMC)

BACKGROUND

Non-invasive prenatal testing (NIPT) is a rapidly developing and widely used method in the prenatal screening. Recently, the widespread use of the NIPT caused a neglecting of the limitations of this technology.

CASE PRESENTATION

The 38-year-old woman underwent amniocentesis because of a high risk of trisomy 2 revealed by the genome-wide Non-Invasive Prenatal Test (NIPT). The invasive prenatal diagnosis revealed the mosaicism for a small supernumerary marker chromosome sSMC derived from chromosome 2. Interphase fluorescence in situ hybridization (FISH) on uncultured amniocytes revealed three signals of centromere 2 in 30% of the cells. GTG-banded metaphases revealed abnormal karyotype (47,XX,+mar[21]/46,XX[19]) and was confirmed by array comparative genomic hybridization (aCGH). Cytogenetic analyses (FISH, aCGH, karyotype) on fetal skin biopsies were performed and confirmed the genomic gain of the centromeric region of chromosome 2. In the placenta, three cell lines were detected: a normal cell line, a cell line with trisomy 2 and a third one with only the sSMC.

CONCLUSION

Whole-genome Non-Invasive Prenatal Testing allows not only the identification of common fetal trisomies but also diagnosis of rare chromosomal abnormalities. Especially in such cases, it is extremely important to perform not only NIPT verification on a sample of material other than trophoblast, but also to apply appropriate research methods. Such conduct allows detailed analysis of the detected aberration, thus appropriate clinical validity.

Evaluation of non-invasive prenatal testing to detect chromosomal aberrations in a Chinese cohort

The aim of this study was to evaluate the clinical feasibility of non‐invasive prenatal testing (NIPT) to detect foetal copy number variations (CNVs). Next‐generation sequencing for detecting foetal copy number variations (CNVs) was performed on the collected samples from 161 pregnancies with ultrasound anomalies and negative NIPT results for aneuploidy. The performance of NIPT for detecting chromosome aberrations was calculated. The sensitivity and specificity of NIPT for detecting CNVs > 1 Mb were 83.33% and 99.34%; the PPV and negative predictive rate (NPV) were 90.91% and 98.68%. Non‐invasive prenatal testing can be performed to detect chromosomal aberrations in first trimester with high performance for CNVs, and occasional discordant cases are unavoidable.

Prenatal and Postnatal Genetic Testing: Why, How, and When?

There have been major advances in genetic testing especially over the last 10 years. We have advanced from looking at simple chromosomes under a microscope to more sophisticated analysis of the DNA makeup of chromosomes and from testing a single gene to sequencing almost all of our genetic material. Similarly, in the field of prenatal testing we have made great strides in screening and diagnostic testing in the hope of detecting significant abnormalities in the fetus while decreasing the risk to the pregnancy. In this article the major types of genetic screening and diagnostic testing, both prenatal and postnatal, will be reviewed. [Pediatr Ann. 2017;46(11):e423-e427.].