OBJECTIVE: To determine if sonographic measurements and ratios are abnormal in fetuses with trisomv 18. STUDY DESIGN: A genetics database was used to identify 24 fetuses at 15-20 weeks gestational age iGA) with a trisomv 18 karyotype. Five sonographic measurements [Biparietal diameter (BPD), head circumference (HQ, Abdominal circumference (AC), lemur length (FL). and cephalic index (CI)] and 3 ratios [BPD/FL, AC/HC, and AC/'FL] from each fetus with trisomv 18 \\ere matched to identical measurements and ratios from 72 control fetuses confirmed to have a normal karyotype. All control fetuses were also matched for GA, race, fetal sex, and maternal age. To control for GA, each measurement was expressed as the number of standard deviations from the mean U-score) of all normal fetuses for that particular GA. Mean /-scores adjusted for matching factors were compared for cases vs controls. Logistic regression and ROC curves were used to determine the best predictors and cut-off points to diagnose trisomv 1H. RESULTS: Mean /-scores for FI. and AC were significant!) lower in cases vs controls and CI and BPD 7FL ratios were significantly increased. AC and CI appeared to be the measurements most sironglv associated with trisomv 18. The mean AC for the trisomv cases was 1.5 standard deviations less than that of the not mal fetuses and the mean CI was 1.1 standard deviations greater than that of the normal group. ROC anahsis for AC and Cl measurements showed that CI had the highes! sensitivity {.7:i) and specificity (.72 with 80.9 being the best cut-off value. CONCLUSIONS: Although several of the measurements studied were significantly different in trisomv IS fetuses versus the control group, our data suggests that sonographic measurements and ratios at ln-20 weeks are not sensitive and specific enough to be useful as a clinical diagnostic lool.
