Researchers followed 164 pregnant women throughout their pregnancies to see how their bone strength changed. They used a special safe scanning technology to measure bone density in the hip area during each trimester. Most women experienced some bone loss during pregnancy, but the amount varied widely. Women who didn’t take calcium, vitamin D, or multivitamins were more likely to lose bone density. Interestingly, women who had been pregnant before tended to lose bone faster. The good news is that these changes appear to be related to nutrition, suggesting that taking the right supplements during pregnancy might help protect bone health.

The Quick Take

  • What they studied: How much bone density pregnant women lose or gain during pregnancy, and what factors affect these changes
  • Who participated: 164 healthy pregnant women who were measured three times—once during each trimester of pregnancy
  • Key finding: Most pregnant women (83%) experienced some bone loss, especially in the second and third trimesters. Women who didn’t take calcium, vitamin D, or multivitamins were significantly more likely to lose bone density.
  • What it means for you: If you’re pregnant or planning to become pregnant, taking calcium and vitamin D supplements may help protect your bone health during pregnancy. This is especially important if you’ve been pregnant before, as previous pregnancies may increase bone loss risk.

The Research Details

This was a prospective cohort study, which means researchers followed the same group of women forward through time and measured them repeatedly. All 164 pregnant women had their hip bone density measured three times using a special scanning technology called REMS (radiofrequency echographic multi-spectrometry). This technology is safe because it doesn’t use radiation like traditional bone scans. Researchers also asked women about their diet, supplements, lifestyle, and pregnancy history.

The women were divided into groups based on whether they lost or gained bone density between their first and third trimesters. Among the 136 women who lost bone, researchers further separated them into those who lost bone slowly versus quickly. This allowed researchers to identify patterns and find out what factors predicted faster bone loss.

This study is important because it’s one of the first to use a safe, radiation-free technology to carefully track bone changes throughout pregnancy. Previous studies couldn’t measure bone density as accurately during pregnancy because they used methods that exposed women and babies to radiation. Understanding how pregnancy affects bones helps doctors give better advice about nutrition during pregnancy and may help prevent bone problems later in life.

This study has several strengths: it followed women throughout their entire pregnancy rather than just taking one measurement, it used a safe and accurate measurement method, and it included a reasonable number of participants. However, the study only measured hip bone density and didn’t look at other bones. The study also didn’t randomly assign women to different supplement groups, so we can’t be completely certain that supplements caused the bone protection—only that they were associated with it. The findings need to be confirmed in larger studies.

What the Results Show

Bone density decreased significantly as pregnancy progressed. Women had stronger bones in their first trimester compared to their second and third trimesters. However, there was huge variation between women—some lost a lot of bone while others lost very little or even gained bone.

The most important finding was that women who didn’t take calcium and vitamin D supplements were much more likely to experience bone loss. Similarly, women who didn’t take any multivitamins were also more likely to lose bone density. These two factors—lack of calcium/vitamin D and lack of multivitamins—were the strongest predictors of bone loss.

Women who had been pregnant multiple times before showed faster bone loss compared to first-time mothers. This suggests that repeated pregnancies may put additional stress on the skeleton.

The study found wide differences between individual women in how much bone they lost. Some women lost bone quickly while others lost it slowly, even though they were all healthy and at similar stages of pregnancy. This variation suggests that factors beyond just nutrition—possibly genetics, physical activity, or other health factors—also play a role in bone changes during pregnancy.

Previous research suggested that pregnancy causes bone loss because the developing baby needs calcium for bone development. This study confirms that bone loss does happen but shows it’s not inevitable and can be reduced with proper nutrition. Earlier studies couldn’t measure bone changes as accurately because they used radiation-based methods that weren’t safe to use repeatedly during pregnancy. This study’s use of radiation-free technology provides clearer evidence than previous research.

The study only measured bone density in one location (the hip/femoral neck) rather than the entire skeleton, so we don’t know if other bones are affected differently. The study didn’t randomly assign women to take or not take supplements—it just observed which women chose to take them. This means we can’t be completely certain that supplements caused the bone protection; it’s possible that women who took supplements had other healthy habits that protected their bones. The study also didn’t follow women after pregnancy to see if bone density recovered. Finally, all participants were healthy women, so results may not apply to women with bone disease or other health conditions.

The Bottom Line

Pregnant women should consider taking calcium and vitamin D supplements during pregnancy. The evidence suggests this may help protect bone density. A typical recommendation would be 1,000-1,200 mg of calcium daily and 600-800 IU of vitamin D daily during pregnancy, but pregnant women should discuss specific supplement needs with their healthcare provider. Taking a prenatal multivitamin also appears beneficial. These recommendations have moderate confidence based on this study, though more research is needed.

This research is most relevant for pregnant women, women planning to become pregnant, and healthcare providers advising pregnant patients. It’s especially important for women who have been pregnant before, as they appear to be at higher risk for bone loss. Women with a history of bone problems or low calcium intake should pay particular attention. This research is less relevant for non-pregnant individuals, though the findings may have implications for bone health across the lifespan.

Bone loss during pregnancy happens gradually across the second and third trimesters. If a woman starts taking calcium and vitamin D supplements early in pregnancy, she may be able to slow or prevent bone loss throughout the pregnancy. However, the study didn’t measure how quickly supplements work, so we don’t know if starting them later in pregnancy is still beneficial. Bone recovery after pregnancy may take months to years.

Want to Apply This Research?

  • Track daily calcium and vitamin D intake (in milligrams and IU respectively) throughout pregnancy. Set a goal of 1,000-1,200 mg calcium and 600-800 IU vitamin D daily, and log actual intake from food and supplements. Include notes about supplement compliance.
  • If not already taking them, start a prenatal vitamin with calcium and vitamin D. Set a daily reminder to take supplements at the same time each day. Log supplement intake in the app to build accountability and identify any missed doses.
  • Track supplement adherence weekly and calculate weekly averages of calcium and vitamin D intake. Monitor for any pregnancy-related symptoms that might affect nutrient absorption. After pregnancy, continue tracking bone-health nutrients and note any changes in energy or bone-related symptoms. Share tracking data with healthcare provider at prenatal visits.

This research provides evidence about bone changes during pregnancy and the potential protective effects of calcium, vitamin D, and multivitamin supplementation. However, this study should not replace personalized medical advice from your healthcare provider. Pregnant women should consult with their obstetrician or midwife before starting any new supplements, as individual needs vary based on diet, health conditions, and other medications. The findings apply to healthy pregnant women and may not apply to women with bone disease, calcium metabolism disorders, or other medical conditions. This research is informational and not a substitute for professional medical diagnosis or treatment.