A mixture model of ductus venosus pulsatility index in screening for aneuploidies at 11-13 weeks' gestation.

OBJECTIVE To assess the value of ductus venosus pulsatility index for veins (DV PIV) in screening for aneuploidies at 11-13 weeks' gestation. METHODS Fetal DV PIV was measured in singleton pregnancies undergoing first-trimester screening for aneuploidies. In euploid (n = 44,756) and aneuploid (202 cases of trisomy 21, 72 cases of trisomy 18 and 30 cases of trisomy 13) fetuses, DV PIV was best described by a mixture model of distributions. Performance of screening for aneuploidies by DV PIV alone and in combination with fetal nuchal translucency (NT) thickness and serum free β-hCG and PAPP-A was estimated. RESULTS In euploid pregnancies there was a bimodal distribution of DV PIV with a dominant crown-rump length (CRL)-dependent part, accounting for around 97% of cases in Caucasians and around 93% in Afro-Caribbeans, and a smaller CRL-independent distribution. In aneuploidies the dominant part was the CRL-independent distribution, which accounted for around 85% cases of trisomies 21 and 18 and 70% of cases of trisomy 13. In screening for trisomy 21 by maternal age, NT and biochemistry at a risk cutoff of 1 in 100, the detection rate was 89.7% and false positive rate was 2.74%; with addition of DV PIV, the values were 93.5 and 1.63%, respectively. CONCLUSIONS Measurement of DV PIV improves the performance of first-trimester combined test for aneuploidies.