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) 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 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 and the GAP method demonstrated an overall mean percent error of 3.1%, an overall absolute error of 240 g, and an overall absolute percent error of 8.0%.  The overall mean absolute percent error among these studies of 8.0% would correspond to a birth weight between 3500 g and 4100 g for a GAP-derived EFW of 3800 g.

The GAP method appears to be an accurate approach to estimate birth weight and accurately predicts birth weight within 10% in a diverse population.