Associations Between Maternal Screen Time Duration, Gestational Weight Gain, and Small-for-Gestational-Age Infants: A Retrospective Clinical Study

Background:Screen use is a common sedentary behavior that may influence gestational weight gain (GWG) and fetal growth through metabolic and sleep-related pathways. However, evidence regarding dose–response relationships, nonlinear thresholds, effect modification by pre-pregnancy body mass index (BMI), and mediation by inadequate GWG remains limited. We aimed to assess the association between maternal screen time and deviations in GWG and small-for-gestational-age (SGA) birth, and to examine dose–response relationships, BMI-related effect modification, and the mediating role of inadequate GWG.Methods:We retrospectively analyzed data of 8162 women in a single-center (2019–2024). Average daily screen time was obtained from questionnaires administered during mid-to-late pregnancy, and outcomes were categorized into three groups according to Institute of Medicine (IOM) guidelines and SGA defined by INTERGROWTH-21st. Multinomial and binomial logistic regression models, adjusted for confounders using multiple imputation, were used to evaluate linear trends, with screen time modeled both as a continuous variable and in quartiles. Restricted cubic splines were applied to characterize dose-response relationships, and BMI-stratified interaction analyses were performed to evaluate effect modification. Causal mediation analysis under the counterfactual framework (with bootstrap sampling) was used to estimate the indirect effect attributable to inadequate GWG, with additional sensitivity analyses and E-value calculations.Results:For each additional hour per day of screen time, the adjusted odds ratios (aORs) for inadequate and excessive GWG were 1.06 and 1.13, respectively (both p < 0.01). Restricted cubic spline analyses showed a clear dose-response relationship, with excessive GWG exhibiting a nonlinear increase at higher exposure levels (p_nonlin = 0.012, aOR ≈ 3). The risk of SGA increased with longer screen time (aOR = 1.08), with an aOR of 1.41 for Q4 versus Q1 (both p < 0.001), and restricted cubic spline analyses suggested mild nonlinearity (p_nonlin = 0.029). Pre-pregnancy BMI showed evidence of effect modification (p_int < 0.05). Mediation analysis under the counterfactual framework indicated that inadequate GWG explained approximately 38% of the statistical association between screen time and SGA. Sensitivity analyses yielded consistent results, with E-values around 1.3–1.5 and all lower bounds >1.20.Conclusion:Longer screen time was associated with an increased risk of abnormal GWG and SGA, with nonlinearity at high exposure levels and heterogeneity by pre-pregnancy BMI. Prenatal care should routinely record and limit screen time exposure, alongside interventions to reduce sedentary behavior, increase physical activity, and improve sleep. Prevention of inadequate GWG should be prioritized to reduce SGA risk, while targeted strategies to prevent excessive GWG are warranted among women with obesity. For practical implementation, a provisional cutoff of ≥4 h/day (approximately the upper quartile range in this cohort) may be used to flag high exposure for targeted counseling, with ≤2 h/day serving as a reference level. These thresholds are exploratory and require external validation.