Limited clinical utility of midtrimester fetal morphometric percentile rankings in screening for birth weight abnormalities.

Abstract

Our purpose was to determine whether midtrimester fetal ultrasonographic morphometric percentile rankings are sensitive screening tests for preterm labor or birth weight abnormalities. Stepwise multiple regression and chi 2 analysis were used to identify midtrimester fetal measurements predicting birth weight and gestational age. Receiver-operator characteristics curves were used to evaluate abdominal circumference percentiles as a test for large-for-gestational-age and small-for-gestational-age infants. Extremes in abdominal circumference and head measurement percentiles were associated with large- and small-for gestational-age infants but not with preterm delivery. Abdominal circumference predicted birth weight in regression analysis; however, receiver-operator characteristic curves showed abdominal circumference percentiles to be poor screening tests for large- or small-for-gestational-age infants. The positive predictive value of 10th and 90th abdominal circumference percentiles for small- and large-for-gestational-age infants was < 20%. Midtrimester percentile rankings offer no clear benefit in targeting fetuses with potential birth weight abnormalities or risk of preterm delivery and may provide clinically misleading information.