Hierarchical Classification of Factors Associated With Noninvasive Prenatal Testing Failures and Its Impact on Pregnancy Outcomes.

Objective: To conduct a hierarchical classification analysis of the nonreportable results of noninvasive prenatal testing in an attempt to reduce failure rates and provide pregnant women with accurate information to alleviate their anxiety.

Methods: In this study, 30,039 singleton pregnancies who underwent noninvasive prenatal testing in a single center from May 2019 to April 2022 were collected, and 811 samples with initial noninvasive prenatal testing failure were retrospectively analyzed. Grouping was based on the reasons for initial test failure; tracking the noninvasive prenatal testing results and prenatal diagnosis results (if any) of the "z-scores in the gray area" group and analyzing the possible influencing factors of the "low fetal fraction" group in the pre-experimental and experimental period by using one-way analysis of variance, Mann-Whitney U test, and χ² test; and tracking the pregnancy outcomes of the test failures samples to analyze the risk of perinatal complications and adverse pregnancy outcomes of the different types of test failures.

Results: None of the samples' initial inconclusive results because of z-scores in the gray area were found to have chromosomal aneuploidy. However, pregnancy complications (P = 0.018) and a high likelihood of adverse pregnancy outcomes (P = 0.048) may still occur. Maternal gestational age (P < 0.001), body mass index (P < 0.001), library concentration (P < 0.001), and fetal gender (P < 0.001) were considered to be the associated factors for the initial low fetal fraction results. This may be associated with pregnancy complications (P < 0.001) and a high likelihood of adverse pregnancy outcomes (P = 0.034). The body mass index (P = 0.015) and time between draws (P = 0.001) were associated with the second test's success. The incidence of low fetal fraction samples was more frequent with blood collection tubes of the G type than with the K type (P < 0.001).

Conclusion: Initial inconclusive results because of z-scores in the gray area did not imply an increased risk of aneuploidy, but vigilance is needed for an increased risk of pregnancy complications and adverse pregnancy outcomes. Because of the low fetal fraction, the initial absence of results may be related to the assay method, as well as the effect of blood collection tubes and the need to be alert to the risk of pregnancy complications and adverse pregnancy outcomes.