Intermittent Fasting During Pregnancy and Neonatal Birth Weight: A Systematic Review and Meta-Analysis.

Background/Objectives: Intermittent fasting (IF), such as Ramadan fasting, is common among pregnant women despite religious exemptions. The possible impact of fasting on pregnancy outcome and, in particular, on birthweight is uncertain and was documented with conflicting evidence. Methods: The aim of this meta-analysis and systematic review was to investigate the association between intermittent fasting during pregnancy and neonatal birthweight, along with low birthweight (LBW, <2500 g) risk. Studies evaluating fasting during pregnancy with reported neonatal outcomes were included. We searched (PubMed, Scopus, Web of Science) from 2004 through June 2025. All contributing studies were observational in design; no randomized trials were identified. The risk of bias was assessed using the Newcastle-Ottawa Scale. The pooled relative risks (RR) and mean differences (MD) were calculated according to random-effects models (DerSimonian-Laird method) and heterogeneity was quantified with the I² statistic. Results: Nineteen studies, all observational in design, were included for qualitative synthesis, and six studies yielded quantitative data to conduct meta-analyses. No randomized controlled trials were identified. Intermittent fasting during pregnancy, encompassing more than 1.3 million pregnancies, was associated with a small but statistically significant reduction in neonatal birth weight. The pooled mean difference was -94 g (95% CI: -176 to -12 g; p = 0.03; I² = 70%), indicating a minor but statistically significant effect that is unlikely to be clinically meaningful. The pooled RR for LBW was 0.96 (95% CI: 0.88-1.05; p = 0.38; I² < 10%), showing no association between fasting and low birthweight risk. Sensitivity analyses reduced heterogeneity (I² ≈ 55%) and confirmed the robustness of these findings. According to the GRADE approach, the certainty of evidence was moderate for birthweight and high for LBW. Conclusions: Intermittent fasting during pregnancy, including Ramadan fasting, was associated with a minor but statistically significant reduction in neonatal birthweight without increasing the risk of low birthweight. This difference was small and clinically negligible. Further prospective studies are needed to clarify trimester-specific effects and long-term developmental outcomes.