Average fetal weekly weight gain: a novel measure of fetal growth velocity

To develop a simplified measure of intrauterine fetal growth velocity from birth weight and gestational age at term.

This concept is based on the observation that intrauterine fetal growth in the third trimester is quasi-linear. The average fetal weekly weight gain (AWG) was calculated by dividing the difference between birth weight (in g) and the 24-week median weight by the difference between gestational age at birth and 24 weeks, as follows: [Formula: see text] An obstetric database of 12,425 term live singleton pregnancies was studied to validate this measure.

The mean AWG was 176.5 g/week, SD 29.1. There was a close correlation between birth weight z-scores and the AWG (R = 0.993). Pregnancy characteristics correlated with the AWG, the strongest being fetal gender and cigarette smoking (p < 0.0001). Females had an AWG 9 g lower than males; multiparae had an AWG 7 g higher. Other significant correlates include maternal weight, height and body mass index.

The AWG is a novel estimate of intrauterine fetal growth velocity that is computationally simple, and could be used as an alternative to the birth weight z-score.