For millions of Muslim families around the world, the holy month of Ramadan is a time of spiritual reflection and fasting from dawn until sunset. But for pregnant women, the question of whether to fast is a deeply personal and often medically considered decision. A study published brings reassuring news for expectant mothers in Indonesia and beyond: prenatal exposure to Ramadan fasting does not appear to influence the age at which their daughters begin menstruation, a key marker of long-term reproductive health.
The research is one of the largest and most rigorous investigations into this topic to date. By analyzing data from over 21,000 Indonesian women, scientists aimed to understand if this form of intermittent fasting during pregnancy could have a lasting impact on the next generation.
Why This Question Matters to Every Family
Age at menarche (AAM)—the age of a girl’s first menstrual period—is more than just a milestone. It is a fundamental indicator of female reproductive health. Studies have shown that the timing of menarche can be linked to future health outcomes, including risks for certain cancers, cardiovascular disease, and bone health. While genetics play a major role, scientists have long been interested in how a mother’s nutrition during pregnancy might “program” her child’s development, a concept known as fetal programming.
Previous research in this area has often focused on extreme situations, such as the Dutch Famine of 1944-1945, where pregnant women faced severe food shortages. However, the reality for most women is different. Many experience milder forms of nutritional changes, like meal-skipping or intermittent fasting, which are common practices across many cultures and religions, not just during Ramadan.
How the Study Worked
Led by researchers from Johannes Gutenberg-University Mainz in Germany, Heidelberg University, and Stanford University, the team used a clever “quasi-experimental” approach. They compared the reported age at menarche of Muslim women whose time in the womb happened to overlap with Ramadan, against those who were not exposed to Ramadan prenatally.
Because the timing of Ramadan shifts each year, a woman’s exposure to it during her pregnancy is essentially random—much like a natural experiment. This method provides powerful insights without the ethical issues of asking pregnant women to change their diets for a study. The researchers drew on two major data sources:
- The Indonesian Family Life Survey (IFLS): A long-running survey following thousands of families.
- The Indonesian Demographic and Health Surveys (DHS): Nationally representative health data.
After carefully cleaning the data to ensure accuracy—for example, by excluding women who were unsure of their menarche date—the final analysis included thousands of women born between 1935 and 1999. The researchers looked not only at any exposure to Ramadan but also at whether the fasting period fell during the first, second, or third trimester of pregnancy, as different stages of development could theoretically be more sensitive.
The Reassuring Results
The study’s core finding is clear and consistent: there is no significant association between prenatal exposure to Ramadan and a daughter’s age at menarche.
Whether a mother’s pregnancy overlapped with Ramadan or not, their daughters began menstruation at statistically the same age. This finding held true no matter which trimester the fasting occurred in. The researchers conducted additional checks, such as looking only at younger women whose memories of their first period were likely more accurate, and the results remained the same.
To make the data easier to understand, here are two tables summarizing the key findings from the study’s main analysis.
Table 1: No Significant Difference in Age at Menarche (IFLS Data)
This table shows the average age at menarche for women in the IFLS sample, comparing those exposed to Ramadan in the womb to those who were not. The “difference” is so small it is statistically meaningless.
| Group | Number of Women | Average Age at Menarche (Years) |
|---|---|---|
| Unexposed to Ramadan in utero | 4,655 | 13.53 |
| Exposed to Ramadan in utero | 3,426 | 13.55 |
| Difference | *+0.02 years (about 7 days)* |
Table 2: Timing of Exposure Doesn’t Matter (DHS Data)
This table from the larger DHS dataset breaks down the exposed group by the trimester of exposure. It confirms that fasting during any stage of pregnancy shows no meaningful effect on the average age of menarche.
| Group | Number of Women | Average Age at Menarche (Years) |
|---|---|---|
| Unexposed to Ramadan in utero | 9,149 | 13.04 |
| Exposed in 1st Trimester | 1,332 | 13.01 |
| Exposed in 2nd Trimester | 1,255 | 13.03 |
| Exposed in 3rd Trimester | 1,368 | 13.01 |
As you can see from the tables, the numbers are remarkably similar across all groups. The tiny differences observed are well within the range of what could happen by chance.
What This Means for Mothers and Doctors
The study’s lead authors emphasize that their findings should not be interpreted as a blanket statement that prenatal nutrition doesn’t matter. Extensive research shows it is critical. However, this study suggests that the specific, relatively mild nutritional alteration of intermittent fasting may not be a key driver in determining the timing of a daughter’s puberty.
This is particularly relevant in Indonesia, the country with the world’s largest Muslim population, where surveys show that between 68% and 82% of pregnant women choose to fast during Ramadan. The findings offer a layer of scientific reassurance for those making this personal choice. Furthermore, because the study’s authors compare Ramadan fasting to common practices like meal-skipping in non-Muslim populations (documented across Asia, the Americas, and Europe), the results have a global relevance.
The researchers note that their findings are consistent with studies on the Dutch famine, which also found no link between that severe prenatal nutritional shock and age at menarche. This consistency across very different contexts—one of extreme deprivation and one of mild, temporary fasting—strengthens the conclusion that menarcheal timing might be robust to these types of prenatal nutritional variations.
In conclusion, this landmark Indonesian study provides a valuable piece of the puzzle in understanding female reproductive health. It suggests that while a healthy diet during pregnancy is essential for many reasons, concerns about intermittent fasting like that during Ramadan are unlikely to have a long-term impact on the specific outcome of a daughter’s age at puberty. For the millions of families navigating this question, the news is one of reassurance, grounded in robust science from their own communities.
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