Objective  To investigate associations of interpregnancy weight change with preterm birth, low birth weight, macrosomia, small for gestational age (SGA), and large for gestational age (LGA).

  Methods  The data on 6 589 pregnant women having two or more singleton live births during 2015 – 2020 and their newborns were extracted from the Maternal and Child Health Information System of Guangdong province. The pregnant women were assigned into four groups according to the changes in their interpregnancy body mass index (BMI) of ＜−1, −1 – ＜1 , 1 – ＜3, and ≥ 3 kg/m². Logistic regression model was used to assess the associations of interpregnancy BMI change with adverse birth outcomes.

  Results  In all the newborns, the proportion was 5.5% for preterm birth, 4.7% for low birth weight, 2.4% for macrosomia, 11.4% for SGA, and 5.4% for LGA, respectively. The results of logistic regression analysis showed that compared to those with the interpregnancy BMI change of −1 – < 1, the pregnant women having the change of 1 – < 3 have an increased risk of giving a birth to a macrosomia (odds ratio OR = 1.66, 95% confidence interval 95% CI: 1.13 – 2.24); the women with the interpregnancy BMI change of 3 and more have an increased risk of giving a birth to a macrosomia (OR = 2.31, 95% CI: 1.42 – 3.70) and to a LGA infant (OR = 1.87, 95% CI: 1.33 – 2.60); while, each increase of 1 kg/m² in interpregnancy BMI is associated with a 7% decreased risk of SGA (OR = 0.93, 95% CI: 0.89 – 0.97). No significant association of interpregnancy BMI change with preterm birth or low birth weight was observed (P > 0.05).

  Conclusion  Pregnant women′s interpregnancy weight gain is associated with increased risks of macrosomia and LGA of their newborns. The results suggest that body weight control during pregnancy and after delivery need to be promoted among pregnant women.