Prenatal paraben exposure and neonatal birth outcomes: The modifying role of mid‑to‑late pregnancy weight gain rate.

Parabens are ubiquitous endocrine-disrupting chemicals. However, the effects of paraben mixtures on neonatal growth and the modifying role of post‑blood‑collection gestational weight gain rate (GWG_after) remain unclear. This prospective cohort included 934 mother-infant pairs from Ningxia, China (2023-2025). Maternal serum concentrations of five parabens (methylparaben, MeP; ethylparaben, EtP; propylparaben, PrP; butylparaben, BuP; heptylparaben, HeP) were measured during mid-pregnancy. GWG_after was classified as below‑recommended, within‑recommended, or above‑recommended based on the IOM 2009 weekly rate recommendations for mid‑to‑late pregnancy. Multiple linear regression assessed individual parabens, while quantile g-computation (qgcomp) evaluated mixture effects, adjusting for covariates. Stratified analyses and interaction terms were used to evaluate effect modification by GWG_after. In the overall population, the paraben mixture was significantly associated with shorter birth length (ψ = -0.050, 95% CI: -0.089, -0.012, P = 0.011). Single-pollutant analyses showed that MeP and PrP were significantly associated with shorter birth length and lower birth length Z‑score in the below‑recommended GWG_after group (P_FDR < 0.05). In qgcomp, the paraben mixture was significantly associated with decreased birth length in the below‑recommended GWG_after group (ψ = -0.117, 95% CI: -0.220, -0.023, P = 0.020), with MeP contributing the largest negative weight. Sensitivity analyses supported the robustness of these findings. These results indicate potential effect modification by GWG_after for MeP and PrP on birth length, with inverse associations predominantly among women with below‑recommended GWG_after across single-pollutant and mixture analyses, supported by formal interaction tests. No significant associations were found between paraben exposure and birth weight in any GWG_after subgroup. These findings highlight the need to consider GWG_after categories in prenatal environmental risk assessment.