Accurate estimation of fetal weight (EFW) is useful for delivery planning and labor management. The gestation-adjusted projection (GAP) method uses third-trimester ultrasound EFW to predict birth weight and assumes that normal fetuses do not cross percentiles on growth curves. The purpose of this systematic review and meta-analysis is to determine the accuracy of extrapolated EFW utilizing the GAP method.

A systematic literature search was performed using MEDLINE/PubMed, Embase, Scopus, and Web of Science for studies published from database inception to June 2023. We queried quantitative studies of pregnant women at term (≥ 37 weeks’ gestation) with a growth ultrasound performed between 34 and 37 weeks. Multiple gestations and fetuses with anomalies were excluded. Studies were eligible for inclusion if the EFW was compared to the actual birth weight. Search terms included “gestation-adjusted projection”, “fetal weight”, “fetal weight extrapolation”, “ultrasound”, and “birth weight”. The quality of studies was evaluated utilizing the Newcastle-Ottawa Scale, and the risk of bias was assessed using the ROBINS-I tool.

A total of eight studies with 5306 subjects met inclusion criteria. Comparisons were made between the EFW and birth weight using mean percent error, mean absolute error, and mean absolute percent error. The mean percent error is the percentage difference between birth weight and the predicted value with the possibility of negative and positive values offsetting one another, while the mean absolute error and the mean absolute percent error is a measure of the absolute difference. Meta-analysis was performed using a random-effects model. The GAP method demonstrated an overall mean percent error of 3.13% (95% CI [1.08, 5.19]), an overall absolute error of 239.94 g (95% CI [205.33, 274.55]), and an overall mean absolute percent error of 8.0% (95% CI [6.88, 9.11]).

The GAP method appears to be an accurate approach to birth weight estimation in a diverse population and predicts birth weight within 10%. Additional studies are needed to assess whether the GAP method improves maternal and neonatal outcomes.