The Effects of Maternal Prepregnancy Obesity and Excessive Gestational Weight Gain on Fetal Growth: A Longitudinal Fetal Growth Study on a Chinese Cohort.

Objective: To evaluate the independent effects of prepregnancy obesity and gestational weight gain on fetal growth patterns and explore whether prepregnancy obesity can modify the association between gestational weight gain and fetal growth trajectories. Methods: A multicenter retrospective cohort was established, consisting of 9075 women with singleton pregnancies across 24 tertiary hospitals in 18 Chinese provinces. Each participant underwent a minimum of three ultrasound examinations between gestational week 12 and the conclusion of pregnancy. Fetal anthropometric measurements included biparietal diameter, abdominal circumference, head circumference, and femur length, with the estimated fetal weight (EFW) calculated using the Hadlock formula. Fetal growth trajectories were modeled using a linear mixed model with cubic splines, adjusted for maternal characteristics. Differences in trajectories were compared across categories of prepregnancy body mass index (BMI) and gestational weight gain. Global and week-specific comparisons were evaluated using the likelihood ratio test and the Wald test, while effect modification was assessed through stratified analysis. Results: Fetal weight was positively associated with prepregnancy BMI and gestational weight gain. From gestational week 12 through week 40, the EFW significantly differed among the offspring of women categorized as underweight, normal weight, overweight, or obese. Specifically, fetuses of women with obesity presented a significantly higher EFW than those of women in the other groups. When stratified by gestational weight gain (inadequate, adequate, and excessive), significant differences in EFW were observed from gestational week 16 until the conclusion of the pregnancy. Stratified analysis indicated that prepregnancy BMI modified the association between gestational weight gain and fetal growth trajectories. In women without obesity, gestational weight gain was significantly and positively associated with EFW and abdominal circumference; however, in women with obesity, gestational weight gain did not demonstrate a significant effect on fetal growth trajectories. Conclusion: Our data showed that prepregnancy BMI and gestational weight gain were positively associated with fetal growth. Furthermore, prepregnancy BMI acted as an effect modifier in the relationship between gestational weight gain and fetal growth trajectories. These findings suggested that weight control before conception carries greater clinical significance than the management of gestational weight gain.