Accuracy of sonographic estimates of fetal weight in very small infants

Abstract

Objective: Fetal outcome is inversely related to gestational age and birth weight. Therefore, in very small fetuses, estimated weight may play an important role in clinical management. Our aim was to determine the accuracy of sonographic estimates of fetal weight in very small infants.

Design: Retrospective chart review.

Subjects: We retrospectively studied 100 consecutive infants with a birth weight of < 1000 g, at a gestational age between 24.0 and 34.0 weeks, in which biometric data < 2 weeks prior to delivery were available for analysis.

Methods: We estimated fetal weight with the use of two methods--by those of Hadlock and colleagues and Scott and colleagues--and compared the estimated values with measured birth weights.

Results: The infants had a mean birth weight of 742 +/- 173 (SD) g, at a gestational age of 28.1 +/- 2.0 (SD) weeks. With Hadlock's method, the mean estimated fetal weight (EFW) was 736 +/- 186 (SD) g, which was not significantly different from birth weight; the mean EFW error was 0.8 +/- 12.7 (SD) %. With Scott's method, the mean EFW was 780 +/- 185 (SD) g, which was significantly increased above birth weight; the mean EFW error was 5.7 +/- 12.5 (SD) %. The accuracy of the weight estimates was not significantly affected by the period between ultrasound examination and delivery if < 2 weeks, or by fetal growth restriction.

Conclusion: In our population of small fetuses, Hadlock's estimates of fetal weight correlated well with measured birth weight, whereas Scott's method tended to overestimate.