The impact of pregnancy on the long-term weight gain of primiparous women in England

Abstract

OBJECTIVES: To investigate the impact of pregnancy on long-term weight gain of primiparous mothers in England, and to identify potential risk factors for maternal obesity. DESIGN: A retrospective, repeat-pregnancy study which examined the change in maternal body weight from the beginning of the first successful pregnancy to the beginning of the second. SUBJECTS: Two hundred and forty-three mothers, all of whom had been weighed during the first trimester of their first and second pregnancies, and none of whom had fallen pregnant less than 12 months after the birth of their first child. MEASUREMENTS: Sociodemographic, behavioural, medical, obstetric and perinatal data, together with antenatal measurements of maternal body weight and height, were extracted from each mother’s obstetric notes. A comprehensive survey of weighing scales used at all antenatal clinics was undertaken. RESULTS: After accounting for the effect of ageing, there was no significant long-term increase in mean maternal body weight following the first pregnancy (95% Confidence Intervals: −0.82–0.28 kg). While most mothers (70.8%) gained 1.0 kg or less, 24.7% gained more than 1.54 kg. Even after accounting for the maximum error in clinic scales, 14.8% of the mothers gained 1.54 kg or more in association with their first pregnancy. Mothers with higher BMIs at the beginning of their first pregnancy, who gained more weight during pregnancy, gave birth to heavier babies and had longer intervals between their pregnancies, gained significantly more weight from one pregnancy to the next. CONCLUSIONS: Pregnancy has little impact on the mean weight gain of primiparous women from England, who have a low prevalence of obesity (BMI≥26.0, 25.5%). Nevertheless, pregnancy may be associated with a permanent increase in maternal body weight simply because it is a period of positive energy balance during which some women gain excessive weight. Other factors, such as prepregnant BMI, determine whether long-term weight gain actually occurs.