Gestational age at delivery differed significantly across PPBMI groups ( p < 0.05), with a decreasing trend observed in higher PPBMI categories; Neonatal birthweight differed significantly across PPBMI groups ( p < 0.05), showing a positive trend with higher PPBMI.
Maternal age varied significantly by PPBMI category ( p < 0.05), showing a positive trend with higher PPBMI; Women in the underweight group were younger, had a lower proportion of advanced maternal age (≥35 y) and exhibited higher prevalences of nulliparity and natural conception ( p < 0.05).
The overall PTB rate was 4.8% ( n = 3, 478), with an increasing trend observed with higher PPBMI: 4.5% ( n = 431) in underweight, 4.5% ( n = 2, 291) in normal weight, 6.1% ( n = 594) in overweight, 7.4% ( n = 162) in obesity.