Introduction Fetal environments play significant roles in determining adult well-being, particularly as they relate to non-communicable diseases and skill formation. We studied gender-specific distributional consequences of fetal environment (in the form of in-utero exposure to Ramadan, the Islamic holy month of fasting), in Indonesia, on birth weights, performance on Raven’s Colored Progressive Matrices (CPM), math scores, hours worked and earnings.

Methods We used quantile regressions to conduct a quantitative comparison of distributional consequences, by gender, of full month exposures to Ramadan in-utero on outcomes of interest. Our data included Muslim children and adults measured during rounds 1 and 4 of the Indonesian Family Life Survey. Our main outcome measures were: birth weights—559 observations (females) and 624 (males); Raven’s CPM scores—1693 (females) and 1821 (males) for 8–15 year olds; math test scores—1696 (females) and 1825 (males) for 8–15 year olds; hours worked—3181 (females) and 4599 (males) for 18–65 year olds; earnings—2419 (females) and 4019 (males) for 18–65 year olds.

Results Full month of exposure to Ramadan in-utero led to significant reductions at the 5% significance level that were concentrated in the bottom halves of the outcome distributions: among 8–15 years, lower scores on Raven’s CPM tests for females (mean: −9.2%, 10thQ: −19%, 25th Q: −19.4%) and males (mean: −5.6%, 10thQ: −12.5%); lower math scores for females (mean: −8.6%, 25thQ: −15.9%) and males (mean: −8.5%, 10thQ: −13.6%); among females 18–65 years, significant reduction in hours worked (mean: −7.5%, 10thQ: − 26.3%).

Conclusion Events during the fetal period have far-reaching consequences for females and males in the lowest (10th and 25th) quantiles of outcome distributions, affecting the ‘relatively poor’ the most. These results call for caution in interpreting studies on child development that rely on mean comparisons alone.