Researchers studied 290 pregnant women in their first three months to understand how common vitamin D deficiency is and what causes it. They found that about 53% of these women didn’t have enough vitamin D in their blood. The study discovered that working outside the home, having multiple pregnancies, using sunscreen, and not taking vitamin D supplements were connected to lower vitamin D levels. The researchers suggest that pregnant women need better nutrition education and should consider taking vitamin D supplements early in pregnancy to protect both their health and their baby’s development.

The Quick Take

  • What they studied: How many pregnant women in their first three months don’t have enough vitamin D in their blood, and what factors might cause this problem
  • Who participated: 290 pregnant women who were in their first trimester (first three months of pregnancy) and visited two hospitals in Iran during 2024
  • Key finding: About 53 out of every 100 pregnant women studied didn’t have adequate vitamin D levels, which is a surprisingly high number
  • What it means for you: If you’re pregnant or planning to become pregnant, getting your vitamin D levels checked early and possibly taking supplements may be important for your baby’s development. Talk to your doctor about whether vitamin D supplementation is right for you.

The Research Details

This was a cross-sectional study, which means researchers took a snapshot in time by collecting information from 290 pregnant women all at once. The women answered questions about their daily habits, diet, work, and sun exposure. Researchers also took blood samples to measure how much vitamin D each woman had in her body. They used a specific blood test that measures a form of vitamin D called 25-hydroxyvitamin D3, which is the best way to check if someone has enough vitamin D.

The researchers used statistical tools to look for patterns in the data. They compared women with low vitamin D to women with normal levels to see what differences existed between the two groups. They looked at factors like whether women worked indoors or outdoors, how many children they’d had before, whether they took vitamin D supplements, how much sun they got, and how much they used sunscreen.

This type of study is useful for understanding how common a health problem is in a specific group of people and what might be causing it. By taking a snapshot of many pregnant women at the same time, researchers can quickly identify patterns without waiting years for results. This helps doctors understand which pregnant women might need extra vitamin D support.

The study included a reasonable number of participants (290 women) and used proper blood tests to measure vitamin D levels. The researchers used appropriate statistical methods to analyze their data. However, because this was a snapshot study done in one region of Iran, the results might not apply exactly the same way to pregnant women in other countries or climates. The study doesn’t prove that these factors cause vitamin D deficiency—it only shows they’re connected.

What the Results Show

The main finding was that 52.8% of the pregnant women studied—roughly 1 out of every 2 women—had low vitamin D levels. This is a very high number and suggests that vitamin D deficiency during early pregnancy is a common problem in this population.

The researchers found several factors connected to low vitamin D. Women who worked outside the home had different vitamin D levels than those who didn’t work or worked indoors. Women who had given birth three or more times before were more likely to have low vitamin D. Women who took vitamin D supplements had higher vitamin D levels than those who didn’t. Women who spent more time in the sun had better vitamin D levels, but interestingly, women who used more sunscreen had lower levels—probably because sunscreen blocks the sun’s rays that help your body make vitamin D.

Surprisingly, eating more foods with vitamin D (like fish, eggs, and fortified milk) didn’t seem to make a big difference in vitamin D levels. However, the researchers noted that overall, the pregnant women weren’t eating many vitamin D-rich foods to begin with.

The study found that sun protection practices (like using sunscreen and wearing protective clothing) were connected to lower vitamin D levels. This makes sense because vitamin D is produced when your skin is exposed to sunlight. The researchers also found that occupational status mattered—women’s jobs affected their vitamin D levels, likely because some jobs keep people indoors more than others.

Previous research has shown that vitamin D deficiency is common in pregnant women worldwide, especially in certain regions and seasons. This study’s finding of 53% deficiency is consistent with what other researchers have found in similar populations. The connection between sun exposure and vitamin D levels matches what we already know about how vitamin D is made in the body. However, the finding that diet didn’t strongly predict vitamin D levels is interesting and suggests that for many pregnant women, supplements or sun exposure may be more important than food sources alone.

This study was done in one region of Iran with 290 women, so the results might not apply the same way to pregnant women in other countries with different climates, cultures, or diets. The study only shows connections between factors and vitamin D deficiency—it doesn’t prove that one thing causes another. The researchers didn’t measure some other factors that might affect vitamin D, like skin color or how much time women spent outdoors. Because this was a snapshot study, we don’t know what happened to these women over time or whether vitamin D supplementation actually improved their pregnancy outcomes.

The Bottom Line

Based on this research, pregnant women should consider getting their vitamin D levels checked early in pregnancy (moderate confidence). If levels are low, vitamin D supplementation appears beneficial and is recommended by the researchers (moderate confidence). Spending safe time in the sun without excessive sunscreen may help, but this should be balanced with skin cancer prevention (low to moderate confidence). Eating more vitamin D-rich foods like fatty fish, egg yolks, and fortified milk is good practice, though it may not be enough on its own (moderate confidence).

This research is most relevant for pregnant women, especially those in their first trimester. Women planning to become pregnant should also pay attention. This is particularly important for women who work indoors, use lots of sunscreen, live in areas with limited sunlight, or have had multiple pregnancies. Women in sunny climates may have different needs than those in cloudier regions. Talk to your doctor about whether these recommendations apply to your specific situation.

Vitamin D levels can be checked with a simple blood test, and results typically come back within days. If you start taking vitamin D supplements, it takes several weeks to months to build up adequate levels in your body. The benefits for your baby’s development happen throughout pregnancy, so starting early is important. You should expect to take supplements throughout your pregnancy and possibly beyond.

Want to Apply This Research?

  • Track daily vitamin D supplement intake (yes/no) and weekly sun exposure time in minutes. Also note any sunscreen use and indoor vs. outdoor work hours to identify patterns in your vitamin D habits.
  • Set a daily reminder to take your vitamin D supplement at the same time each day (such as with breakfast). If you work indoors, schedule 15-20 minutes of outdoor time during lunch when possible, balancing sun exposure with skin protection. Log these activities in the app to build consistency.
  • Check vitamin D levels with your doctor at the beginning of pregnancy and again in the second or third trimester to see if supplementation is working. Use the app to track supplement adherence and sun exposure patterns over weeks and months. Share this data with your healthcare provider to adjust your vitamin D plan if needed.

This research describes patterns found in one study of 290 pregnant women and should not replace personalized medical advice from your doctor. Vitamin D levels, needs, and supplementation recommendations vary by individual based on many factors including location, skin type, diet, and pregnancy health. Always consult with your healthcare provider before starting any supplements during pregnancy. This study shows associations but does not prove that vitamin D deficiency causes pregnancy complications. Pregnant women should not increase sun exposure significantly without discussing skin cancer prevention with their doctor. The findings may not apply equally to all populations or geographic regions.