In this cohort that included 6264 women, about a quarter increased while 5% lowered their BMI category between their first and second pregnancies. Approximately half gained ≥1 kg/m2, of which one-third had excess gain of ≥3 kg/m2; only 10% lost >1 kg/m2 between pregnancies. Overall, BMI tended to change among women who birthed their second child in the first two years after the first delivery, and was stable among women who birthed their second child later, regardless of the initial weight status. Interpregnancy BMI gain was associated with increased risks of LGA, GDM and emergency Caesarean delivery in the second pregnancy. Conversely, an increased risk of low birthweight was observed in women with BMI loss between their first two pregnancies. When the results were further stratified by BMI in the first pregnancy, a higher risk of emergency Caesarean delivery was evident in women with a BMI <23 kg/m2 experiencing interpregnancy BMI gain, while higher risks of low birthweight and SGA were evident in women with a BMI ≥23 kg/m2 experiencing interpregnancy BMI loss.
The interpregnancy period is a valuable opportunity to address pregnancy complications and optimise health for the next pregnancy and the rest of the life-course. Despite recommendations to return to pre-pregnancy weight between 6 and 12 months postpartum, with the goal of a normal BMI , about half the women in our study increased their BMI during the first two years post-delivery instead. A study conducted among Caucasians also showed similar findings, where almost 20% of normal-weight women became overweight or obese in their next pregnancy, whereas more than 90% of overweight or obese women maintained their status in the next pregnancy . This highlights the urgent need to implement intervention strategies that include targeted lifestyle modifications to prevent increased BMI during the interpregnancy period.
Interpregnancy BMI gain and the associated increased risks of subsequent LGA, GDM and emergency Caesarean delivery are consistent with previous studies [9,10,20]. These adverse complications could be the result of 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 increased risk of emergency Caesarean delivery in women with an initial BMI <23 kg/m2 is consistent with a recent meta-analysis , suggesting increased susceptibility of lean women to subsequent delivery complications in response to weight gain between pregnancies. However, the indications for emergency Caesarean delivery were unclear in our data and should be further examined in future studies. Similarly, interpregnancy BMI gain has been associated with increased risks of hypertensive disorders [9,25] and stillbirth , but we were unable to analyse these outcomes due to 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 nationwide efforts 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 had 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 . Another study also showed that a decrease in BMI >1 kg/m2 was associated with low birthweight (<2500 g) . 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 .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 . However, our study observed that women with BMI ≥23 kg/m2 who 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 that 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 a significant reduction in risk 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 . This was highlighted by a recent study that showed that metabolic health status, rather than BMI, played a greater role in fecundability . Therefore, interpregnancy BMI loss may not truly reflect the metabolic health status of our study participants, which confounds the positive effects of weight loss in overweight and obese women. Furthermore, changes in body composition and fat distribution between pregnancies in these overweight or obese women can impact 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 post-delivery likely represents the best window of opportunity to intervene to return to pre-pregnancy BMI, regardless of initial weight status. Effective lifestyle interventions that aim to limit postpartum weight retention and maintain a stable interpregnancy BMI during this window are crucial to improving perinatal outcomes. Such interventions should ideally be engaging, grounded by behaviour change theories, and integrate components of both diet and physical activity . An electronic health intervention for postpartum women with excessive GWG resulted in restrained eating, along with decreased uncontrolled eating and energy intake . However, other behaviours such as emotional eating, physical activity, and sedentary time remain unchanged . To improve the success of lifestyle interventions, it is essential to identify additional facilitators and barriers faced by these women. Although these were identified among overweight and obese women trying to conceive ,it remains unclear whether such findings are applicable to women of normal weight.
This is the first study to investigate the distribution and outcomes of interpregnancy weight change in Asian women, with a substantial sample size of women from the three largest ethnicities in Singapore (Chinese, Malay, and Indian) and results that are likely generalizable to the Asian population. In addition, the study used gestational-age-adjusted BMI, which provides an accurate interpregnancy BMI assessment. However, since BMI is an imperfect measurement of metabolic health , future studies should investigate how other markers of metabolic health, such as insulin resistance, lipid profile and body composition, are associated with adverse perinatal outcomes. The GDM screening policy underwent a transition during the study period, from a risk-based 2-point OGTT between 2015-2017 to a universal 3-point OGTT from 2018-2020, thus, the incidence of GDM may be underestimated in the earlier years [39,40]. We did not account for the socioeconomic status and lifestyle habits of the women in the analysis due to the lack of data from medical records. Finally, long-term outcomes of these women and their offspring were not available to provide insights on their long-term health.