Objective: Previous studies on weight gain in pregnancy suggested that maternal weight on average increased by 0.5-2.0 kg in the first trimester of pregnancy. This study examined whether mean maternal weight or body composition changes in the first trimester of pregnancy.
Design: Prospective observational study.
Population: We studied 1,000 Caucasian women booking for antenatal care in the first trimester of pregnancy.
Setting: Large university teaching hospital.
Methods: Maternal height and weight were measured digitally in a standardized way and Body Mass Index (BMI) was calculated. Maternal body composition was measured using segmental multifrequency Bioelectrical Impedance Analysis (BIA). Sonographic examination confirmed the gestational age and a normal ongoing singleton pregnancy in all subjects.
Main outcome measures: Maternal weight, maternal body composition.
Results: The mean BMI was 25.7 kg/m(2) and 19.0% of the women were in the obese category (> or =30.0 kg/m(2)). Cross-sectional analysis by gestational age showed that there was no change in mean maternal weight, BMI, total body water, fat mass, fat-free mass or bone mass before 14 weeks gestation.
Conclusions: Contrary to previous reports, mean maternal weight and mean body composition values remain unchanged in the first trimester of pregnancy. This has implications for guidelines on maternal weight gain during pregnancy. We also recommend that calculation of BMI in pregnancy and gestational weight gain should be based on accurate early pregnancy measurements, and not on self-reported or prepregnancy measurements.