Association of maternal pre-pregnancy body mass index with adverse
pregnancy outcomes according to maternal age: a population-based cohort
study
Abstract
Objective To clarify the association of pre-pregnancy body mass index
(BMI) with adverse pregnancy outcomes according to maternal age in a
large and diverse population in China. Design Retrospective cohort
study. Setting Guangdong Province, China. Population 669101 women
participated in the National Free Preconception Health Examination
Project in Guangdong Province, China, from 2013 to 2017. Methods BMI
were calculated and classified into four categories according to Chinese
criteria: underweight (BMI <18.5kg/m2), normal weight
(18.5-23.9kg/m2), overweight (24.0-27.9kg/m2), and obesity (≥28.0kg/m2).
Main outcome measures Outcomes were preterm birth (PTB), large for
gestational age (LGA), small for gestational age (SGA), primary
caesarean delivery, shoulder dystocia or birth injury, and stillbirth.
Log-binomial models were employed to estimate the adjusted risk ratios
(RRs) and 95% confidential intervals (95%CIs) for underweight,
overweight and obesity. Results The incidence ratios PTB, LGA, SGA,
primary caesarean delivery, shoulder dystocia or birth injury and
stillbirth were 5.0%, 11.2%, 9.7%, 14.5%, 1.1% and 1.2‰,
respectively. Overall, compared with normal BMI, underweight was
associated with increased risk of PTB (adjusted RR 1.06, 95%CI
1.04-1.09) and SGA (1.23, 1.22-1.26); overweight was associated with the
increased risk of LGA (1.17, 1.14-1.19), primary caesarean delivery
(1.18, 1.16-1.20) and stillbirths (1.44, 1.03-2.06); and obesity was
associated with increased risk of PTB (1.12, 1.05-1.20), LGA (1.32,
1.27-1.37), primary caesarean delivery (1.45, 1.40-1.50). These
associations were different according to maternal age. Conclusion
Maternal pre-pregnancy abnormal BMI were associated with the risks of
adverse pregnancy outcomes among Chinese population, but the risks
differed according to maternal age.