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

Abstract

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

Methods: 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: $\text{AWG}=\frac{\text{BWT}-670}{\text{GA}-24}.$

An obstetric database of 12 425 term live singleton pregnancies was studied to validate this measure.

Results: 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.

Conclusions: 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.

Keywords:

• Birth weight
• fetal growth
• fetus

Declaration of interest

The authors report no conflicts of interest.