First‐trimester screening for trisomies by cfDNA testing of maternal blood in singleton and twin pregnancies: factors affecting test failure

ABSTRACT Objective To examine factors affecting the rate of failure to obtain a result from cell‐free DNA (cfDNA) testing of maternal blood for fetal trisomies 21, 18 and 13 in singleton and twin pregnancies in the first trimester. Methods This was a prospective study of 23 495 singleton and 928 twin pregnancies undergoing screening for fetal trisomy by targeted cfDNA testing at 10 + 0 to 14 + 1 weeks' gestation. Multivariate logistic regression analysis was used to determine significant predictors of failure to obtain a result after first sampling. Results There was no result from cfDNA testing after first sampling in 3.4% (798/23 495) of singletons, 11.3% (91/806) of dichorionic twins and 4.9% (6/122) of monochorionic twins. Multivariate logistic regression analysis demonstrated that the risk of test failure, first, increased with increasing maternal age (odds ratio (OR), 1.02; 95% CI, 1.01–1.04) and weight (OR, 1.05; 95% CI, 1.04–1.05), decreasing gestational age (OR, 0.85; 95% CI, 0.79–0.91), serum pregnancy‐associated plasma protein‐A (PAPP‐A) multiples of the median (MoM) (OR, 0.56; 95% CI, 0.49–0.65) and free β‐human chorionic gonadotropin (β‐hCG) MoM (OR, 0.67; 95% CI, 0.60–0.74), second, was higher in women of black (OR, 1.72; 95% CI, 1.33–2.20) and South Asian (OR, 1.99; 95% CI, 1.56–2.52) than those of white racial origin, in dichorionic twin than in singleton pregnancy (OR, 1.75; 95% CI, 1.34–2.26) and in pregnancies conceived by in‐vitro fertilization than in those conceived naturally (OR, 3.82; 95% CI, 3.19–4.55) and, third, was lower in parous than in nulliparous women (OR, 0.63; 95% CI, 0.55–0.74). Conclusions Maternal age, weight, racial origin and parity, gestational age, dichorionicity, method of conception and serum levels of free β‐hCG and PAPP‐A are independent predictors of cfDNA test failure. The risk of test failure is higher in dichorionic twin than in singleton pregnancies, mainly because a higher proportion of twins are conceived by in‐vitro fertilization and more of the women are nulliparous. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.