Researchers studied how exercise affects the placenta—the organ that feeds a baby during pregnancy. Seventy-six pregnant women either exercised three times a week or didn’t exercise. Scientists measured special proteins in the placenta after birth. Women who exercised had different levels of these proteins compared to those who didn’t exercise. Interestingly, some changes only happened when the baby was female. The findings suggest that staying active during pregnancy may help the placenta work better, though more research is needed to understand exactly how this helps babies.

The Quick Take

  • What they studied: Does exercising during pregnancy change how the placenta develops and functions, and does it matter if the baby is male or female?
  • Who participated: 76 pregnant women (average age 33) were split into two groups: 40 women who exercised and 36 who didn’t. The exercising group did 60-minute workouts three times per week from week 17 of pregnancy until birth.
  • Key finding: Women who exercised had higher levels of a growth protein (G-CSF) in their placenta and lower levels of two other proteins (EGF and IL-1ra). These changes were even more noticeable when the baby was female.
  • What it means for you: Exercise during pregnancy may improve how the placenta works, which could benefit both mother and baby. However, this is one study, so talk to your doctor before starting any exercise program during pregnancy. The benefits appear strongest for pregnancies with female babies, though more research is needed.

The Research Details

This was a controlled experiment where pregnant women were divided into two groups. One group exercised three times per week for 60 minutes each session, combining aerobic exercise (like walking or cycling) with strength training. The other group continued their normal routines without the structured exercise program. Both groups were followed from week 17 of pregnancy until delivery. After the babies were born, researchers examined the placentas and measured 13 different proteins that help the placenta develop and function. They used advanced technology called Luminex profiling to measure these proteins accurately.

The researchers also tracked other factors like how much weight the mothers gained, their diet, sleep patterns, activity levels, and fitness improvements. This allowed them to understand not just whether exercise made a difference, but potentially why it made a difference.

The study was designed to look for differences between the exercise and control groups, and also to see if results varied based on whether the baby was male or female, and whether the mother was overweight before pregnancy.

The placenta is like a life-support system for the developing baby. Understanding how exercise changes the placenta’s chemistry helps us know whether exercise is truly beneficial during pregnancy and how it works. By measuring specific proteins, scientists can see the actual biological changes happening, not just guess based on outcomes. This approach is stronger than just asking women how they feel.

This study has several strengths: it randomly assigned women to exercise or control groups (reducing bias), it had a reasonable sample size of 76 women, and it used precise laboratory technology to measure placental proteins. However, the study is relatively small, and results from one study need confirmation by other researchers. The findings about female babies versus male babies are interesting but need more investigation since this wasn’t the main focus of the study.

What the Results Show

Women who exercised during pregnancy had measurably different placental protein levels compared to women who didn’t exercise. Specifically, exercising mothers had higher levels of G-CSF (a growth-promoting protein) and lower levels of EGF and IL-1ra (two other proteins). These differences were statistically significant, meaning they’re unlikely to be due to chance.

When researchers looked at whether the baby’s sex mattered, they found something interesting: the exercise effects on G-CSF and TNF-α (an inflammation protein) were only seen in pregnancies with female babies. Additionally, pregnancies with female babies showed a trend toward lower IL-6 levels (another inflammation protein) in mothers who exercised, though this wasn’t quite statistically significant.

The researchers also discovered that controlled weight gain during pregnancy appeared to explain part of why exercise changed G-CSF levels. In other words, exercising mothers gained weight more gradually, and this slower weight gain was connected to the higher G-CSF levels.

The study found that exercise didn’t significantly change all 13 proteins measured—only a few showed clear differences. This suggests that exercise has targeted effects on specific placental functions rather than changing everything. The fact that some effects appeared only in female pregnancies suggests that fetal sex may influence how the placenta responds to exercise. Maternal weight status before pregnancy (whether women were normal weight, overweight, or obese) didn’t seem to strongly modify the exercise effects, though the study wasn’t specifically designed to test this.

Previous research has shown that exercise during pregnancy is safe and beneficial for mothers and babies, but scientists haven’t fully understood the biological mechanisms. This study adds important information by showing that exercise actually changes the placenta’s chemical environment. The specific proteins measured in this study are known to be important for placental development, so these findings suggest exercise may improve placental function. However, most previous studies haven’t looked at these specific proteins, so direct comparisons are limited.

The study had several limitations worth noting. First, it’s relatively small with only 76 women, so results need confirmation in larger studies. Second, the study only measured placental proteins at birth—we don’t know if these changes happen throughout pregnancy or just at the end. Third, the findings about female versus male babies are interesting but weren’t the main focus, so they need dedicated research to confirm. Fourth, the study didn’t follow babies long-term to see if the placental changes actually led to better health outcomes. Finally, the study population was relatively homogeneous (similar ages and backgrounds), so results might not apply equally to all pregnant women.

The Bottom Line

Based on this research, moderate-intensity exercise (both aerobic and strength training) during pregnancy appears safe and may benefit placental function. Current guidelines already recommend 150 minutes of moderate-intensity exercise per week during pregnancy for women without contraindications. This study provides additional biological support for those recommendations. However, always consult your healthcare provider before starting or continuing an exercise program during pregnancy, as individual circumstances vary. Confidence level: Moderate—this is one well-designed study, but more research is needed.

Pregnant women and those planning pregnancy should care about this research, especially those interested in optimizing their pregnancy health. Healthcare providers may find this useful when counseling pregnant women about exercise. Women expecting female babies may be particularly interested, though the differences between male and female pregnancies need more study. This research is less relevant for women with pregnancy complications or medical conditions that limit exercise—they should follow their doctor’s specific guidance.

The changes measured in this study happened over the course of pregnancy (from week 17 to delivery). You wouldn’t notice these placental changes yourself—they’re only visible through laboratory analysis. Benefits for the baby might include better placental function throughout pregnancy and at birth, but long-term health benefits need to be studied. If you start exercising during pregnancy, focus on consistency rather than expecting immediate results.

Want to Apply This Research?

  • Track weekly exercise sessions (aim for 3 sessions of 60 minutes combining cardio and strength training) and monitor gestational weight gain against your healthcare provider’s recommended range. Log the type of exercise, duration, and how you felt during and after.
  • Use the app to schedule three weekly exercise sessions during pregnancy and set reminders. Include both aerobic activities (walking, swimming, stationary cycling) and gentle strength training. Track completion rates and adjust intensity based on how you feel, always staying within your doctor’s guidelines.
  • Monitor consistency of exercise throughout pregnancy (weeks 17 onward), track weight gain patterns to ensure it stays within recommended ranges, and note any changes in energy levels or pregnancy symptoms. Share this data with your healthcare provider at prenatal visits to ensure the exercise program remains appropriate.

This research describes biological changes in the placenta associated with exercise during pregnancy but does not prove that these changes directly improve baby health outcomes. Always consult with your obstetrician or healthcare provider before starting, continuing, or modifying an exercise program during pregnancy. This is especially important if you have pregnancy complications, medical conditions, or previous pregnancy losses. The findings apply to healthy pregnancies without contraindications to exercise. Individual responses to exercise vary, and what works for one person may not work for another. This summary is for educational purposes and should not replace professional medical advice.