Accuracy of clinical fetal weight estimation by Midwives.

Background: Clinical fetal weight estimation is a common practice in obstetrics. This study aims to evaluate the accuracy of fetal weight estimation by midwives, and to identify factors that may lead to overestimation or underestimation of fetal weight.

Methods: A cohort prospective study in a Lebanese university hospital, included weight estimation of singleton pregnancies above 35 weeks. Multiple pregnancies, unclear dating, growth retardation, malformations and stillbirths cases are excluded. The estimated fetal weight is recorded by midwives in a sealed envelope and compared to true weight later. The effects of BMI, weight gain, parity, diabetes, hypertension, neonate's sex and weight, uterine contractions, rupture of membranes and daytime or nighttime shift on these estimations were assessed.

Results: One hundred and sixty-six patients were included. Mean birth weight was 3246 ± 362 g. Mean absolute percentage error of weight estimation was 8.5 ± 6.7% (0-30.9%). Estimation was within the correct range of ±10% in 63% of cases. Maternal and fetal factors did not significantly change weight estimation. Fetuses with birth weights more than 4000 tended to be underestimated by midwives. Estimation improved over time (nonsignificant).

Conclusions: Maternal and fetal factors, except for macrosomia, have limited impact on estimation of fetal birth weight. Macrosomia is challenging because of a consistent tendency of underestimation by midwives.