Noninvasive Prenatal Screening Based on Second-Trimester Ultrasonographic Soft Markers in Low-Risk Pregnant Women

Background: We aimed to assess the clinical application of noninvasive prenatal screening (NIPS) based on second-trimester ultrasonographic soft markers (USMs) in low-risk pregnant women.Methods: Data of pregnant women between April 2015 and December 2019 were retrospectively analyzed. Pregnant women [age at expected date of confinement (EDC) of <35 years; low risks for trisomy 21 (T21) and trisomy 18 (T18) based on maternal serum screening; presenting second-trimester USMs (7 types)] who successfully underwent NIPS and had available follow-up information were included in our study. Cases with positive NIPS results were prenatally diagnosed. All patients were followed up for 6 months to 2 years after NIPS, and their clinical outcomes were obtained. Subgroup analyses were performed according to the different USMs.Results: NIPS suggested that among a total of 10,023 cases, 37 (0.37%) were at high risk of aneuploidy, including 4 T21, 6 trisomy 13 (T13), and 27 sex chromosome abnormalities (SCA). Ten cases with aneuploidy (0.10%) were confirmed by prenatal diagnosis, consisting of two T21 and eight SCA. The eight fetuses with SCA consisted of one monosomy X, two XXY, one XXXY, one XXX, one XYY, and two mosaicisms. T21 was detected in one fetus with absent or hypoplastic nasal bone and one fetus with echogenic intracardiac focus (EICF). SCA was detected in five fetuses with EICF, two fetuses with multiple soft markers, and one fetus with echogenic bowel. The positive rate of chromosomal aneuploidy was significantly higher in fetuses with absent or hypoplastic nasal bone (6.25 vs. 0.10%, p = 0.017), echogenic bowel (3.7 vs. 0.10%, p = 0.029), and multiple soft markers (0.678 vs. 0.10%, p = 0.045) than in the total fetuses. The positive predictive values (PPVs) of NIPS in these three groups were 100%, 50%, and 100%, respectively. EICF accounted for 93.25% (9,346/10,023) of the study population, whereas the PPV of NIPS was only 20%.Conclusion: NIPS is an advanced screening test for low-risk pregnant women. In the 10,023 pregnant women sampled, SCA were more common than autosomal trisomy, and EICF was the most frequent USM but the least predictive aneuploidy. Further aneuploidy evaluation is suggested for low-risk pregnant women whose ultrasound indicates absent or hypoplastic nasal bone, echogenic bowel, or multiple soft markers. NIPS can serve as a second-line complementary screening for these women.

Clinical Utility of Noninvasive Prenatal Screening for Rare Chromosome Abnormalities in Singleton Pregnancies

Objective: To systematically investigate the clinical utility of noninvasive prenatal screening (NIPS) commercially used for the common fetal aneuploidies as a prenatal screening tool for rare chromosome abnormalities (RCAs). Design: Prospective study. Setting: Hospital-based. Population or Sample: 528 gravidas with positive NIPS results for RCAs. Methods: Gravidas with positive NIPS results for RCAs subsequently underwent amniocentesis for single nucleotide polymorphism array (SNP-array) were recruit. The degrees of concordance between NIPS and SNP-array were classified into full concordance, partial concordance, discordance related and discordance. Main Outcome Measures: The positive predictive values (PPVs) for rare aneuploidies and segmental imbalances, while incidental findings for regions of homozygosity/uniparental disomy (ROH/UPD), were used to evaluate the performance of NIPS. Results: Of the 528 gravidas with positive NIPS results, 29.2% were confirmed with positive prenatal SNP-array results (154/528). The PPVs for rare aneuploidies and segmental imbalances were 6.1% (7/115) and 21.1% (87/413), respectively. ROH/UPDs, as incidental findings, have been identified in 9.5% (50/528) of gravidas with positive NIPS results. The PPV for clinical significant findings was 8.9% (47/528), including 7 cases with mosaic rare aneuploidies, 35 with pathogenic/likely pathogenic copy number variants, and 5 with imprinting disorders. Conclusions: NIPS commercially used for the common fetal aneuploidies yielded low PPV for rare aneuploidies, moderate PPV for segmental imbalances, and incidental findings for ROH/UPD. For the low PPV for clinical significant findings, NIPS has limited clinical utility for RCAs. Prenatal SNP-array should be regarded as the first-tier test for positive NIPS, particularly for those involved imprinted chromosomes.

The Optimal Cutoff Value of Z-scores Enhances the Judgment Accuracy of Noninvasive Prenatal Screening

ObjectiveTo evaluate the accuracy of Z-scores of noninvasive prenatal screening (NIPS) in predicting 21, 18 trisomy, and X chromosome aneuploidy.MethodsA total of 39,310 prenatal women were recruited for NIPS from September 2015 to September 2020. Interventional prenatal diagnosis was applied to verify the diagnosis of NIPS-positive results. Logistic regression analysis was employed to relate the Z-scores to the positive predictive value (PPV) of NIPS-positive results. Using receiver operating characteristic (ROC) curves, we calculated the optimal cutoff value of Z-scores to predict fetal chromosome aneuploidy. According to the cutoff value, NIPS-positive results were divided into the medium Z-value (MZ) and high Z-value (HZ) groups, and PPV was calculated to access the accuracy of Z-scores.ResultsA total of 288 effective values of Z-scores were used as the final data set. The logistics regression analysis revealed that Z-scores were significantly associated with true-positive results for 21 trisomy (T21) and 18 trisomy (T18) (P < 0.05), whereas the same was not observed for X chromosome aneuploids (P > 0.05). The optimal cutoff value of the Z-score for T21, T18, XO, XXX, and XXY indicated by ROC curve analysis were 5.79, 6.05, −9.56, 5.89, and 4.47, and the area under the curve (AUC) were 0.89, 0.80, 0.48, 0.42, and 0.45, respectively. PPV in the HZ group was higher than that in the MZ group, and the application of the cutoff value reduced the false discovery rate (FDR), which was only 2.9% in the HZ group compared with 61.1% in the MZ group for T21 and T18. The difference in total PPV between the MZ and HZ groups for X chromosome aneuploids was statistically significant. Moreover, the PPV for XXX and XXY seemed to increase with Z-scores but not for XO.ConclusionThe Z-score is helpful for the accurate judgment of NIPS results and for clinical prenatal counseling. Especially for T21 and T18, Z-scores have an excellent clinical association, which is superior to that seen with X chromosome aneuploids. In addition, using Z-scores to judge NIPS results offers a certain reference value for XXX and XXY but not for XO.