Beyond maternal weight: Independent contributions of paternal and maternal obesity to fetal macrosomia in a Peruvian nationwide survey.

INTRODUCTION

Fetal macrosomia is associated with short- and long-term perinatal complications. Although the role of maternal obesity is well established, the father's independent contribution has been less studied, particularly in middle-income countries such as Peru, where the prevalence of parental obesity has increased steadily over the past decade.

OBJECTIVE

To evaluate the association between obesity in both parents and fetal macrosomia in father-mother-newborn triads nationwide in Peru.

METHODS

Analytical cross-sectional study using data from the Peruvian Demographic and Family Health Survey (ENDES) 2015-2024 (excluding 2020). We assembled 30,593 triads with complete information. Exposures were paternal and maternal obesity (body mass index [BMI] ≥30 kg/m2); the outcome was fetal macrosomia (>4000 g). We estimated weighted prevalences, prevalence ratios (PRs) using Poisson regression with robust variance, dose-response curves using restricted cubic splines, and multiplicative interactions.

RESULTS

The prevalence of macrosomia was 6.7% (95% confidence interval [CI]: 6.2-7.2). Obesity affected 22.7% of fathers and 26.2% of mothers. After multivariable adjustment, paternal obesity (PR 1.30; 95% CI: 1.11-1.53) and maternal obesity (PR 1.71; 95% CI: 1.48-1.97) were independently associated with macrosomia. The dose-response gradient was steeper in mothers (overweight PR 1.55; obesity PR 2.26) than in fathers (significant from obesity onward, PR 1.26). A suggestive multiplicative interaction was observed when both parents had obesity (PR 1.38; 95% CI: 1.01-1.90).

CONCLUSIONS

Obesity in both parents was independently associated with fetal macrosomia, with a biologically coherent dose-response gradient and a tendency toward synergy when both exposures coexisted. This pattern supports incorporating paternal nutritional status into obstetric risk stratification and into strategies to prevent adverse perinatal outcomes.