Pregnancy weight gain by gestational age and BMI in Sweden: a population-based cohort study.

BACKGROUND: Pregnancy weight-gain z score charts have recently been proposed as a new tool for classifying gestational weight gain and establishing the link between weight gain and adverse maternal and infant outcomes. However, existing charts are few in number, were based on small sample sizes, and were not population based.
OBJECTIVE: We created population-based pregnancy weight-gain-for-gestational-age z score charts for Swedish women who were stratified by early pregnancy body mass index (BMI).
DESIGN: Serial prenatal electronic medical records were obtained from women who were receiving obstetrical care in the Swedish counties of Gotland and Stockholm. The study population was restricted to nonanomalous, singleton, term pregnancies with no prepregnancy hypertension or diabetes. A multilevel linear regression was used to express the repeated weight-gain measurements as a function of gestational age in underweight, normal-weight, overweight, and obese class I-III women. Observed weight-gain ranges were contrasted with current Institute of Medicine (IOM) pregnancy weight-gain recommendations.
RESULTS: A total of 711,615 serial prenatal weight measurements from 141,767 pregnant women were included. The smoothed means, SDs, and selected percentiles (3rd, 10th, 50th, 90th, and 97th) of weight gain were estimated for each week of gestation. The total weight gain and rate of weight gain decreased with increasing prepregnancy BMI. In all BMI categories, the observed range of pregnancy weight gain was considerably broader than the range currently recommended by the IOM.
CONCLUSIONS: The presented population-based pregnancy weight-gain charts can be used to express maternal weight gain as gestational age-standardized z scores with early pregnancy BMI taken into consideration. The z scores can be used to obtain a better understanding of the relation between pregnancy weight gain and maternal and infant health complications.