Screening for birth weight deviations by second and third trimester ultrasound scan

The aim of this article was to predict small for gestational age (SGA, at or less than the fifth birth weight percentile) and large for gestational age (LGA, at or greater than the 95th birth weight percentile) fetuses by using maternal and fetal parameters from the second and third trimester ultrasound examinations.

This article is a retrospective cohort study on 1979 singleton pregnancies that had a routine 20 to 24 weeks anomaly and a 30 to 34 weeks growth ultrasound scans. SGA delivered before 30 gestational weeks were excluded.

Second trimester estimated fetal weight (EFW2 ), uterine arteries pulsatility index (PI), and maternal pregnancy characteristics were predictive for SGA (SGA second trimester model: R(2)  = 0.225, area under the curve [AUC] = 0.815) and LGA (LGA second trimester model: R(2)  = 0.203, AUC = 0.793). Third trimester EFW (EFW3 ), EFW2 , uterine arteries PI2 , umbilical PI, and maternal pregnancy characteristics improved the prediction of SGA (SGA combined model: R(2)  = 0.423, AUC = 0.896) and LGA (LGA combined model: R(2)  = 0.383, AUC = 0.882). Contingent screening with risk stratification by the second trimester model performed equally well for SGA (AUC = 0.882) and LGA (AUC = 0.861) as the combined models.

Second trimester model performs well in the prediction of SGA and LGA. The addition of third trimester scan offers substantial improvement. Contingency screening is feasible with similar effectiveness.