Combining nuchal translucency with umbilical Doppler velocimetry for detecting fetal trisomies in the first trimester of pregnancy

Objective The aim of our study was to evaluate whether the combined use of umbilical artery pulsatility index (UAPI) and nuchal translucency (NT) measurements would be useful in the prediction of fetal chromosomal abnormalities at 10 to 13 weeks of gestation. Design A prospective study. Population and methods Five hundred and fifty-three consecutive women with singleton pregnancies between 10 and 13 weeks of gestation, who underwent chorionic villus sampling at our institution. UAPI and fetal NT thickness were measured immediately before the invasive procedure. Pregnancies in which structural malformations had been detected by ultrasound were excluded. Results Using the 95th centile and 3 mm as the cutoffs for UAPI and NT, respectively, the detection rate for all chromosomal anomalies was 84.2%, with a false positive rate (1-specificity) of 6.6%, a positive predictive value of 31.3%, and a negative predictive value of 99.4%. Out of the 553 tested pregnancies 502 had both parameters within the normal range and only three of them (0.6%) were chromosomally abnormal; in six of the eight cases (75%) in which both parameters were abnormal a chromosome anomaly was present. Of the 43 cases in which only one parameter was abnormal, 10 were chromosomally abnormal (23.2%). Conclusions Our results suggest that the presence of chromosomal anomalies may be strongly suspected when an increased NT thickness (NT greater than or equal to 3 mm) is associated with an abnormally high UAPI at 10 to 13 weeks of gestation. The number of cases studied is small, however, and these conclusions are tentative and preliminary. The value of a single measurement of NT and UAPI for screening purposes needs to be substantiated by further investigation.