Researchers studied 215 pregnant women in Mexico City to understand how eating and sleeping patterns affect the timing of birth. They found that women who ate late at night (after 9 PM) were nearly six times more likely to have babies born early (before 37 weeks). The study also discovered that getting less than 6 hours of sleep and not taking prenatal vitamins regularly increased early birth risk. While these findings are interesting, they come from one group of women and need to be confirmed with larger studies before doctors change their recommendations.

The Quick Take

  • What they studied: Whether the timing of when pregnant women eat and sleep affects the chances of having a baby born too early (before 37 weeks of pregnancy).
  • Who participated: 215 healthy pregnant women living in Mexico City who were part of a larger health study. Researchers tracked their eating patterns and sleep schedules during all three trimesters of pregnancy.
  • Key finding: Pregnant women who ate food late at night (between 9 PM and 6 AM) had about a 15.5% chance of early birth, compared to only 5.6% for those who didn’t eat late. Women who slept less than 6 hours per night also had much higher early birth rates (63.2% vs. 29.1%).
  • What it means for you: If you’re pregnant or planning to become pregnant, this research suggests that maintaining regular meal times (avoiding late-night eating), getting adequate sleep, and taking prenatal vitamins consistently may help reduce the risk of early delivery. However, this is one study and more research is needed before making major changes to your routine—talk to your doctor first.

The Research Details

This was an observational study, meaning researchers watched and recorded what pregnant women naturally did rather than asking some women to change their habits. The researchers collected information about what the women ate using 24-hour food recalls (asking women to remember everything they ate in the previous day) during each three-month period of pregnancy. They also asked about sleep schedules and recorded whether women ate during nighttime hours. The researchers then compared these eating and sleeping patterns between women who had early births and those who didn’t.

The study tracked several other factors that might affect early birth, including whether women developed pregnancy complications like gestational diabetes or high blood pressure, how much weight they gained during pregnancy, and whether they took prenatal vitamins. By looking at all these factors together, the researchers tried to figure out which ones were most important for early birth risk.

The researchers used statistical methods to calculate the odds—essentially, how much more likely early birth was for women with each eating or sleeping pattern compared to women without that pattern.

Understanding when pregnant women eat and sleep is important because these daily habits affect hormones and body processes that could influence pregnancy length. Previous research has shown that eating at unusual times can affect metabolism and inflammation in the body. This study is valuable because it’s one of the first to look specifically at nighttime eating during pregnancy and early birth risk, which hasn’t been studied much before.

This study has some strengths: it tracked women throughout their entire pregnancy and collected detailed information about their eating patterns. However, there are important limitations to consider. The study included only 215 women from one city in Mexico, so the results may not apply to pregnant women in other countries or with different backgrounds. The study couldn’t prove that late-night eating actually causes early birth—only that the two things happen together. Women who eat late at night might also have other habits or health conditions that increase early birth risk. Additionally, only 19 women in the study had early births, which is a relatively small number for drawing strong conclusions.

What the Results Show

The main finding was that nighttime eating significantly increased the risk of early birth. Among the 71 women (33% of the group) who ate during nighttime hours, 15.5% had early births. In contrast, only 5.6% of women who didn’t eat at night had early births. When researchers used statistical analysis to account for other factors, they found that nighttime eating increased the odds of early birth by nearly 6 times.

Short sleep duration was another major finding. Women who slept less than 6 hours per night had a 63.2% rate of early birth, compared to 29.1% for women who slept more. This was one of the strongest associations in the study. When adjusted for other factors, short sleep increased the odds of early birth by about 4.5 times.

Prenatal vitamin use also mattered significantly. Women who took prenatal vitamins in only 0-1 trimesters (low consumption) had a 25% early birth rate, while those who took them in all 3 trimesters (high consumption) had only a 7.5% rate. Low vitamin consumption increased early birth odds by nearly 8 times compared to high consumption.

Preeclampsia (a serious pregnancy complication involving high blood pressure) was also strongly associated with early birth, increasing the odds by 9 times. However, other factors like maternal age, obesity, and gestational diabetes were not significantly associated with early birth in this study.

The study found that the average time women waited between their last meal and first meal the next day was about 11.8 hours. The average time from waking up to eating breakfast was about 104 minutes, and the average time from dinner to sleep was about 112 minutes. These timing measures weren’t strongly associated with early birth risk when analyzed individually, suggesting that the specific pattern of eating late at night was more important than these general timing measures. The study also found that gestational complications (pregnancy-related health problems) occurred in 16.3% of the women, and about 55.8% of women took prenatal vitamins consistently throughout all three trimesters.

This research adds to a growing body of evidence suggesting that the timing of eating (called ‘chrononutrition’) affects health outcomes. Previous studies have shown that eating late at night is associated with weight gain, metabolic problems, and inflammation in non-pregnant populations. This study extends that research to pregnancy, suggesting that timing of eating may be particularly important during this sensitive period. The findings about sleep duration align with other research showing that adequate sleep is crucial for healthy pregnancy outcomes. However, very few studies have specifically examined nighttime eating during pregnancy, so this research fills an important gap.

Several important limitations should be considered. First, this was a relatively small study with only 215 women from one city, so results may not apply to other populations. Second, only 19 women had early births, which is a small number for statistical analysis. Third, the study couldn’t prove cause-and-effect—it only showed that nighttime eating and early birth occurred together. Women who eat late at night might also have other unmeasured habits or conditions that cause early birth. Fourth, the study relied on women’s memory of what they ate, which can be inaccurate. Fifth, the researchers couldn’t control for all possible factors that might affect early birth risk, such as stress, physical activity, or infections. Finally, the study was observational, meaning women weren’t randomly assigned to eat at different times, so we can’t be certain about the direction of the relationship.

The Bottom Line

Based on this research, pregnant women may benefit from: (1) Avoiding eating between 9 PM and 6 AM—try to finish dinner at least 2-3 hours before bedtime (moderate confidence); (2) Aiming for at least 6-7 hours of sleep per night (moderate confidence); (3) Taking prenatal vitamins consistently throughout all three trimesters (moderate confidence). These recommendations are based on one study and should be discussed with your healthcare provider, especially if you have specific health conditions or dietary needs.

These findings are most relevant to pregnant women or women planning pregnancy, particularly those who currently eat late at night or have short sleep duration. Women with a history of early birth or pregnancy complications should definitely discuss these findings with their doctor. However, these results may not apply equally to all populations, and individual circumstances vary greatly. Men, non-pregnant women, and people in different geographic regions should not assume these findings apply to them.

If a pregnant woman makes changes to her eating and sleep schedule, the benefits would likely accumulate throughout pregnancy rather than appearing immediately. The most critical periods for these habits may be the second and third trimesters, when early birth becomes more of a concern. Realistic expectations would be to see potential benefits over weeks to months of consistent habit changes, not days.

Want to Apply This Research?

  • Track the time of your last meal each day and your total sleep duration. Set a goal to finish eating by 8 PM and aim for 7+ hours of sleep. Log these daily and review weekly to see if you’re meeting targets.
  • Set a phone reminder for 8 PM as your ’eating cutoff time.’ If you’re hungry after that, drink water or herbal tea instead. For sleep, set a consistent bedtime 7-8 hours before your wake time and track actual sleep using your phone or a wearable device.
  • Create a simple weekly dashboard showing: (1) percentage of days you finished eating by 8 PM, (2) average nightly sleep duration, (3) prenatal vitamin doses taken. Review trends monthly to identify patterns and adjust habits as needed. Share results with your healthcare provider at prenatal visits.

This research suggests an association between nighttime eating and early birth risk, but cannot prove cause-and-effect. These findings come from one study of 215 women and should not replace personalized medical advice from your healthcare provider. Pregnant women should not make significant changes to their diet or sleep habits based solely on this research. If you are pregnant or planning pregnancy, discuss your eating patterns, sleep schedule, and prenatal vitamin use with your doctor or midwife. This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.