Interpretation
The interpregnancy period is a valuable opportunity to address complications that have developed during pregnancy and optimise their health for the next pregnancy and for the rest of the life-course. Despite recommendations to return to pre-pregnancy weight between 6 and 12 months postpartum, with the goal to achieve a normal BMI,18 about half of the women in our study had an increase in BMI during the first two years after delivery instead. Almost 30% of women who were of normal weight subsequently became overweight or obese in their next pregnancy, while more than 90% who were overweight or obese remained the same. Indeed, three-quarters of women with an initial BMI of 27.5-29.9 kg/m2 had increased BMI to ≥30 kg/m2 in their second pregnancy (data not shown). A study conducted among Caucasians also showed similar findings, in which almost 20% of women of normal weight became overweight or obese in their next pregnancy, whereas more than 90% of overweight or obese women maintained their status in the next pregnancy.19 These alarming numbers highlight the urgent need to implement intervention strategies including targeted lifestyle modifications to prevent an increase in BMI during the interpregnancy period.
The results on interpregnancy BMI gain and the increased risks of subsequent LGA, GDM and emergency caesarean delivery are consistent with previous studies.9, 10, 20 These adverse complications could be due to reduced insulin sensitivity due to interpregnancy weight gain accompanied by body fat rather than muscle gain, which is common among Asians.19, 21-24 The heightened risk of emergency caesarean delivery in women with an initial BMI <23 kg/m2 is consistent with a systematic review and meta-analysis by Oteng-Ntim et al.21, suggesting that lean women could be more susceptible to subsequent delivery complications in response to weight gain between pregnancies. However, the indications for emergency caesarean delivery were not clear in our data and should be further examined in future studies. Similarly, interpregnancy BMI gain has also been associated with an increased risk of hypertensive disorders9, 25 and stillbirth10, but we could not analyse these outcomes due to our limited sample size or incomplete outcome data. In view of multiple adverse pregnancy outcomes, long-term obesity, and related health risks in women and their offspring, our study, together with many others,12, 26-31 calls for a nationwide effort to break the vicious cycle of interpregnancy weight gain and poor metabolic health.
We found that offspring of women with BMI loss between their first two pregnancies were at a higher risk of low birthweight. This is supported by a study on interpregnancy weight change among women in three consecutive pregnancies, showing that weight loss was associated with an increased risk of low placental weight and SGA births.32 Another study also showed that a decrease in BMI >1 kg/m2 was associated with low birthweight (<2500 g).33 This phenomenon could be explained by insulin sensitivity induced by weight loss, resulting in less glucose crossing the placenta, which contributed to an increased risk of small fetal size.21 A meta-analysis showed that interpregnancy weight loss and SGA was only apparent in women with initial BMI <25 kg/m2, but not among those with BMI ≥25 kg/m2.10 In contrast, we observed that women with BMI ≥23 kg/m2who lost weight during the interpregnancy interval were at a higher risk of low birthweight and SGA, compared to those with BMI <23 kg/m2 in the first pregnancy. This may be attributed to the greater weight loss among women who were overweight or obese within the interpregnancy interval of 1-2 years, compared with women who were lean (BMI loss 1.9 vs 1.5 kg/m2, p<0.001). In addition, unlike other studies which showed a reduction in the risk of adverse pregnancy outcomes among overweight and obese women who lost weight,10, 19-21 our study did not find any significant risk reduction among women with BMI ≥23 kg/m2 who lost weight. Despite the current emphasis on BMI, it represents a crude measure of adiposity and an imperfect assessment of metabolic health.34 This was highlighted by a recent study that showed that metabolic health status, rather than BMI, played a greater role in fecundability.35Therefore, interpregnancy BMI loss may not truly reflect the metabolic health status of those in our study, which may possibly confound the positive effects of weight loss in overweight and obese women. Furthermore, changes in body composition and fat distribution between pregnancies in these women who were overweight or obese may impact on subsequent pregnancy outcomes. This points to the need to investigate the metabolic profile and body composition of women in future studies of interpregnancy weight change and associated outcomes.
Taken together, maintaining a stable interpregnancy BMI is recommended, instead of losing weight between pregnancies. Based on the trend of interpregnancy BMI change, the first two years after delivery likely represents the best window of opportunity to intervene to return to pre-pregnancy BMI, regardless of initial weight status. Effective lifestyle interventions aimed at limiting postpartum weight retention and maintaining a stable interpregnancy BMI during this window are crucial to improve perinatal outcomes. Such interventions should ideally be engaging, grounded by behaviour change theories, and integrate components of both diet and physical activity.36Recently, Bijlholt et al.37 adopted an electronic health approach for postpartum women with excessive GWG, resulting in restrained eating as well as decreased uncontrolled eating and energy intake. However, there was no change in other behaviours such as emotional eating, physical activity, and sedentary time.37 To improve the success of lifestyle interventions, it is essential to identify additional enablers and barriers faced by these women. Although Ku et al. 38 identified potential enablers and barriers among overweight and obese women trying to conceive, it remains unclear whether such findings are applicable to women of normal weight.