How common is substantial weight gain after pregnancy?

Background: Although population-based studies indicate that on average, women gain 1-2kg between pregnancies, women with obesity often attribute its development to childbearing. There is little contemporary data available regarding how commonly this occurs, particularly in women of different body mass index (BMI) categories. The aim of this study was to examine inter-pregnancy weight changes among women at a tertiary obstetric hospital in Melbourne, Australia.

Methods: This was a retrospective review of data from the Birthing Outcomes System electronic record of 19,617 women aged 20 years or older, who delivered at least two consecutive singleton infants at ≥37 weeks' gestation at Mercy Hospital for Women between December 1994 and December 2015. A logistic regression model was used to assess the relationship between gain of ≥4kg/m between pregnancies and maternal BMI category in the first pregnancy, adjusting for covariates of maternal age, inter-pregnancy interval, and socioeconomic status.

Results: Gain of ≥4kg/m between the first two pregnancies occurred in 7.5% of normal weight women, 10.5% of overweight women, and 13.4% of women with obesity. One in five women who were normal weight in their first pregnancy increased to overweight or obese BMI categories in their second pregnancy.

Conclusions: Substantial weight gain in relation to pregnancy affects a considerable proportion of women. Since inter-pregnancy weight gain is associated with several complications in the next pregnancy and longer term, avoiding excessive weight gain during and between pregnancies may prevent adverse health consequences in mothers and offspring.