Distribution of interpregnancy BMI change
Figure 1 shows the cross-sectional trends of BMI change over the interpregnancy interval by weight status at 12 weeks of gestation in the first pregnancy. Overall, BMI tended to change (increase or decrease) among women who had the second delivery in the first two years after the first, and was stable at that level among women who delivered later, regardless of the initial weight status. Figure 2A shows the comparisons of interpregnancy BMI change and weight status at 12 weeks gestation in the first pregnancy. Women who were overweight and obese in their first pregnancy tended to have interpregnancy BMI loss or gain as compared to those who were underweight and normal weight, who tended to be BMI stable (p<0.001).
In total, 24.5% of women gained weight between pregnancies and progressed to a higher BMI category; while 5.4% of women lost weight and dropped to a lower BMI category. Although at least 90% of women who were overweight or obese in the first pregnancy remained at least overweight in the second pregnancy, nearly two-thirds of women with normal weight and half of women who were underweight remained in the same weight status in the first and second pregnancies (Figure 2B ). Similar distributions of interpregnancy BMI change status and weight status in the second pregnancy were observed across weight status in the first pregnancy based on the WHO conventional cut-offs(Table S2) .