RECEIVER-OPERATOR CHARACTERISTIC CURVES FOR THE ULTRASONOGRAPHIC PREDICTION OF SMALL-FOR-GESTATIONAL-AGE FETUSES IN LOW-RISK PREGNANCIES

OBJECTIVE: Our purpose was to assess the accuracy of third-trimester u ltrasonographic biometry in the diagnosis of small-for-gestational age fetuses in a low-risk obstetric population. STUDY DESIGN: A total of 1000 low-risk pregnancies were prospectively examined at 31 weeks' ges tation. The diagnostic accuracy of the fetal abdominal circumference a nd estimated fetal weight according to 24 formulas in the literature w ere evaluated by the use of receiver-operator characteristic curves. R ESULTS: The incidence of a birth weight <10th percentile was 8.2%. The diagnostic accuracies of abdominal circumference and estimated fetal weight were remarkably similar. None of the 24 formulas performed sign ificantly better than the measurement of the abdominal circumference. At a specificity of 90%, 46% of infants with a birth weight <10th perc entile and five of six cases with adverse perinatal outcomes were pred icted. CONCLUSION: In a low-risk obstetric population third-trimester ultrasonographic biometry has limited value in predicting small-for-ge stational-age fetuses, and estimation of fetal weight does not carry a n advantage over measurement of the abdominal circumference. The optim al cutoff value remains uncertain. However, by accepting a 10% false-p ositive rate, half of small-for-gestational-age fetuses and most perin atal complications could be recognized.