Effect of maternal weight on accuracy of maternal and physician estimate of fetal weight.

Objective: To test if maternal and physician clinical fetal weight estimates differ significantly from actual birth weight and if it is affected by maternal weight.

Study Design: A total of 112 term gravidas who presented for induction or elective cesarean were prospectively observed. Prior to physician evaluation, each subject estimated the weight of her baby. Prepregnancy weight, date of most recent ultrasound that estimated fetal weight, and physician clinical estimation of fetal weight were recorded. Birth weight was recorded and compared to estimates.

Results: Maternal and physician mean absolute error (MAE) values did not differ significantly within any body mass index category. Physician MAE values trended higher in class III obese women (477.1 +/- 292.0 g vs. 356.3 +/- 226.8, p = 0.08). Maternal-predicted and birth weight table-predicted MAE did not differ significantly, although table-predicted 50th percentile MAE values trended higher in class II obese women (462.2 +/- 322.4 g vs. 330.8 +/- 275.7, p = 0.07) and in class III obese women (471.5 +/- 363.7 g vs. 356.3 +/- 226.8, p = 0.12). Physician mean percent error trended higher than maternal values in class III obese women (13.6% +/- 9.3 vs. 9.9% +/- 6.4, p = 0.06).

Conclusion: There was a strong trend showing that women with class III obesity were more accurate than their physician in predicting the actual birth weight of their baby.