Impact of overweight, obesity, and gestational weight gain on fetal somatometry, birth weight, and pregnancy complications

Objective
We aimed to investigate fetal somatometric changes and neonatal birth weight (NBW) in babies of women with overweight and grade I–III obesity compared to controls with normal weight.

Methods
We conducted a retrospective cohort study at a Mexican hospital between 2021 and 2023 in otherwise healthy pregnant women with different baseline body mass index (BMI) classifications: normal weight, overweight, grade I obesity, and grade II–III obesity. We used analysis of variance and Cohen's d to compare the area under the curve (AUC) of fetal biometric parameters, as well as NBW. Gestational weight gain (GWG) and obstetric complications were also analyzed. Subanalysis with two-way analysis of variance was performed to contrast the effects of maternal BMI and GWG on fetal growth.

Results
A total of 253 pregnant women were included. Small effect sizes were observed for initial maternal BMI on the AUC of fetal biometry (d > 0.2); there was no significant effect on NBW. The AUC of amniotic fluid index decreased as maternal BMI increased (P = 0.048), and overweight women had a higher incidence of obstetric hemorrhage (P = 0.046). There was a significant effect of GWG on NBW (P = 0.039) and no interaction with baseline BMI (P = 0.744), with smaller babies in mothers with less-than-appropriate versus appropriate GWG (P = 0.050, d = 0.31).

Conclusion
Maternal BMI can have a small effect on fetal somatometry but not on NBW, while GWG affect birth weight regardless of baseline BMI. Patients that were overweight had higher incidence of obstetric hemorrhage. Patients should receive timely prenatal interventions to ensure neither excessive nor insufficient GWG.