Qinzheng Chen,1 Zhen He,1 Yaxin Wang,2 Xuanjin Yang,2 Nana Liu,2 Suhan Zhang,2 Liangkun Ma,2 Xuezhong Shi,1 Xiaocan Jia,1 Yongli Yang,1 Yin Sun,2 Yuan He3 

1Department of Epidemiology and Biostatistics, College of Public Health, Zhengzhou University, Zhengzhou, People’s Republic of China; 2Department of Obstetrics and Gynecology, National Clinical Research Center for Obstetric & Gynecologic Diseases, Peking Union Medical College (PUMC) Hospital, Chinese Academy of Medical Sciences (CAMS) and PUMC, Beijing, People’s Republic of China; 3National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, People’s Republic of China

Correspondence: Yin Sun, Department of Obstetrics and Gynecology, Peking Union Medical College (PUMC) Hospital, Chinese Academy of Medical Sciences (CAMS) and PUMC, Beijing, 100730, People’s Republic of China, Email yinsun_pumch@163.com Yongli Yang, Department of Epidemiology and Biostatistics, College of Public Health, Zhengzhou University, Zhengzhou, 450001, People’s Republic of China, Email ylyang377@zzu.edu.cn

Purpose: To assess the impact of maternal pre-pregnancy body mass index (BMI) on longitudinal fetal growth, and the potential mediation effect of the maternal fasting plasma glucose in first trimester.
Methods: In this retrospective cohort study, we collected pre-pregnancy BMI data and ultrasound measurements during pregnancy of 3879 singleton pregnant women who underwent antenatal examinations and delivered at Peking Union Medical College Hospital. Generalized estimation equations, linear regression, and logistic regression were used to examine the association between pre-pregnancy BMI with fetal growth and adverse neonatal outcomes. Mediation analyses were also used to examine the mediating role of maternal fasting plasma glucose (FPG) in first trimester.
Results: A per 1 Kg/m² increase in pre-pregnancy BMI was associated with increase fetal body length Z-score (β 0.010, 95% CI 0.001, 0.019) and fetal body weight (β 0.017, 95% CI 0.008, 0.027). In mid pregnancy, pre-pregnancy BMI also correlated with an increase Z-score of fetal abdominal circumference, femur length (FL). Pre-pregnancy BMI was associated with an increased risk of large for gestational age and macrosomia. Mediation analysis indicated that the associations between pre-pregnancy BMI and fetal weight in mid and late pregnancy, and at birth were partially mediated by maternal FPG in first trimester (mediation proportion: 5.0%, 8.3%, 1.6%, respectively).
Conclusion: Maternal pre-pregnancy BMI was associated with the longitudinal fetal growth, and the association was partly driven by maternal FPG in first trimester. The study emphasized the importance of identifying and managing mothers with higher pre-pregnancy BMI to prevent fetal overgrowth.

Keywords: body mass index, fetal growth, adverse neonatal outcomes, fasting plasma glucose, mediation analysis, cohort study