ArticlesInterpregnancy weight change and risk of adverse pregnancy outcomes: a population-based study
Introduction
The increasing prevalence of obesity worldwide has prompted WHO to designate obesity as one of the most important global health threats.1 The epidemic is especially pronounced in young people; in the USA, for example, 28% of women aged 20–39 years are obese.2
The adverse effect of maternal overweight and obesity on the outcome of pregnancy has been suspected for more than 50 years.3 Large population-based epidemiological studies indicate that high prepregnancy weight or body-mass index (BMI) confers an increased risk of maternal and perinatal complications, including pre-eclampsia, gestational diabetes, caesarean delivery, macrosomia, and stillbirth.4, 5, 6, 7, 8, 9, 10, 11 Although these associations are biologically plausible and the risks seem to increase with the degree of overweight, suggesting that there is a dose-response effect,4, 7, 11 the possibility that overweight and obesity share common causes with the outcomes cannot be ruled out. Therefore, causal inference for these associations is still regarded as being speculative.11
The argument for a causal association between maternal overweight and adverse pregnancy outcomes would be strengthened if the frequency of these endpoints proved related to changes in exposure over time—ie, that risks were determined by the gain or loss of weight before pregnancy. In a nationwide Swedish cohort study, we examined whether changes in BMI between the beginning of the first and start of the second pregnancies were associated with risks of pre-eclampsia, gestational diabetes, caesarean delivery, stillbirth, and large-for-gestational-age births during the second pregnancy.
Section snippets
Participants
The population-based Swedish Birth Register contains information about demographic characteristics, reproductive history, anthropometry (weight and height from 1992 onwards), and smoking habits, recorded at the first antenatal visit. Between 1990 and 1998, 93–95% of pregnant women in Sweden attended antenatal care before their 15th week of gestation.12, 13, 14 Complications during pregnancy and delivery are registered when the woman is discharged from hospital and classified according to
Results
On average, women gained just over half a BMI unit (median 0·7, IQR −0·3 to 1·7) during a mean interpregnancy interval of 24 months (median 20, IQR 13–31). Weight gain between pregnancies decreased with age, education, height, and BMI at the first pregnancy, and was lower in women of Nordic origin; and increased with smoking at the first pregnancy, the interpregnancy interval, and adverse outcomes during the first pregnancy, including pre-eclampsia, gestational hypertension, caesarean delivery,
Discussion
The findings from this large, prospective population-based study show that weight gain during the interpregnancy interval, as estimated from the difference between first-trimester weights, is strongly associated with the risk of major maternal and perinatal complications, independent of whether women are overweight or not. The gain of 1–2 BMI units only during an average 2 years would increase the risk of gestational hypertension, gestational diabetes, or large-for-gestational-age birth by an
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