Association between maternal gestational weight gain and preterm birth according to body mass index and maternal age in Quzhou, China

The aim of this study is to investigate the association between maternal gestational weight gain (GWG) and preterm birth according to pre-pregnancy body mass index (BMI) and maternal age. We did a cohort, hospital-based study in Quzhou, South China, from 1 Jan 2018 to 30 June 2019. We selected 4274 singleton live births in our analysis, 315 (7.4%) of which were preterm births. In the overall population, excess GWG was significantly associated with a decreased risk of preterm birth compared with adequate GWG (adjusted OR 0.81 [95% CI 0.72-0.91]), and the risk varied by increasing maternal age and pre-pregnancy BMI. Interestingly, underweight women who older than 35 years with excess GWG had significantly increased odds of preterm birth compared with adequate GWG in underweight women aged 20-29 years (2.26 [1.06-4.85]) and normal weight women older than 35 years (2.23 [1.13-4.39]). Additionally, low GWG was positively and significantly associated with preterm birth overall (1.92 [1.47-2.50]). Among normal weight women category, compared with adequate GWG women aged 20-29 years did, those older than 20 years with low GWG, had significantly higher odds of preterm birth, which increased with maternal age (1.80 [1.16-2.79] in 20-29 years, 2.19 [1.23-3.91] in 30-34 years, 3.30 [1.68-6.46] in >> 35 years). In conclusion, maternal GWG was significantly associated with the risk of preterm birth, but the risk varied by pre-pregnancy BMI and maternal age.