Researchers studied nearly 9,000 pregnant women to understand how minerals in their diet affect the risk of premature birth (babies born before 37 weeks). They found that women who didn’t get enough phosphorus in their second trimester or calcium throughout pregnancy had a higher chance of delivering early. The study also showed that taking calcium supplements, especially in the third trimester, appeared protective. These findings suggest that paying attention to mineral intake before and during pregnancy could be an important way to help prevent premature births.

The Quick Take

  • What they studied: Whether the amount of calcium and phosphorus a pregnant woman eats, and whether she takes calcium supplements, affects her chances of having a premature baby.
  • Who participated: 8,897 pregnant women in China (880 who had premature babies and 8,017 who had full-term babies). Researchers interviewed them about their diet during pregnancy.
  • Key finding: Women who didn’t get enough phosphorus in their middle pregnancy had about 30% higher risk of premature birth. Women who didn’t take calcium supplements in their final trimester or didn’t eat enough calcium before and during pregnancy also had higher premature birth risk.
  • What it means for you: If you’re planning to get pregnant or are currently pregnant, making sure you get enough calcium and phosphorus through food or supplements may help reduce the chance of premature birth. However, this is one study and shouldn’t replace advice from your doctor.

The Research Details

This was a case-control study, which means researchers looked backward at two groups of women: those who had premature babies and those who didn’t. They then compared what these women ate during pregnancy to see if there were differences. The researchers conducted one-on-one interviews with pregnant women about their diet and created a database of what they ate. They used statistical tools to figure out whether low mineral intake was connected to premature birth risk.

The study took place at a hospital in China from March 2018 to March 2019. Women were asked detailed questions about their food intake, and researchers tracked whether their babies were born early or on time. This approach allowed scientists to look for patterns between nutrition and birth outcomes.

Case-control studies are useful for studying rare outcomes like premature birth because researchers can focus on comparing women who experienced the outcome with those who didn’t. By asking detailed questions about diet, researchers could identify specific nutrients that might matter. This type of study is considered stronger evidence than simply observing what people eat without following outcomes.

The study included a large number of women (nearly 9,000), which makes the findings more reliable. Researchers used detailed dietary interviews rather than quick questionnaires, which provides better information about what women actually ate. They also used advanced statistical methods to account for other factors that might affect premature birth risk. However, because this is a case-control study looking backward, it cannot prove that low mineral intake directly causes premature birth—only that there’s a connection.

What the Results Show

The main finding was that low phosphorus intake during the second trimester (weeks 13-27 of pregnancy) was linked to a 30% higher risk of premature birth. This means if 100 women with low phosphorus intake were compared to 100 women with adequate intake, about 30 more in the low-intake group might have premature babies.

The study also found that women who didn’t take calcium supplements during the third trimester (final weeks of pregnancy) had increased premature birth risk. Additionally, women who didn’t eat enough calcium before getting pregnant or during pregnancy showed higher risk.

Interestingly, the researchers found that calcium, phosphorus, and calcium supplements seemed to work together—having all three at adequate levels appeared more protective than having just one or two adequate.

The study examined the relationship between these minerals and premature birth across different stages of pregnancy. The findings were strongest for the second and third trimesters, suggesting that mineral intake becomes increasingly important as pregnancy progresses. The researchers also looked at whether the relationship was linear (more is always better) or curved, finding that there may be an optimal range of intake rather than a simple ‘more is better’ pattern.

Previous research has suggested that maternal nutrition affects premature birth risk, but this study provides more specific evidence about phosphorus and calcium. Some earlier studies focused mainly on calcium, but this research highlights that phosphorus may be equally important. The findings align with general medical knowledge that minerals are essential for fetal development and pregnancy health, though this study provides stronger evidence for these specific nutrients.

Because this study looked backward at what women ate, it relied on their memory of their diet, which may not be perfectly accurate. The study was conducted in one hospital in China, so results might not apply to all populations worldwide. The study shows an association between low mineral intake and premature birth but cannot prove that low intake directly causes premature birth—other factors could be involved. Additionally, the study didn’t measure actual blood levels of these minerals, only dietary intake.

The Bottom Line

Women planning pregnancy or currently pregnant should aim to get adequate calcium and phosphorus through diet or supplements. Good sources of calcium include dairy products, leafy greens, and fortified foods. Phosphorus is found in meat, fish, eggs, and dairy. Taking a prenatal vitamin with calcium, especially in the third trimester, appears beneficial. However, these recommendations should complement, not replace, guidance from your healthcare provider. (Confidence level: Moderate—based on one large study, but not yet confirmed by multiple studies)

Pregnant women and women planning to become pregnant should pay attention to these findings. Women with dietary restrictions that limit calcium or phosphorus intake should be especially attentive. However, women should discuss personalized recommendations with their doctor, as individual needs vary. These findings are less relevant for non-pregnant individuals.

The protective effect of adequate mineral intake would develop over weeks and months of pregnancy, not immediately. The study suggests that starting before pregnancy and maintaining adequate intake throughout pregnancy is important. Benefits in terms of reduced premature birth risk would be measured across the entire pregnancy, not in days or weeks.

Want to Apply This Research?

  • Track daily calcium and phosphorus intake in milligrams. Set a goal of 1,000-1,200 mg calcium and 700-1,000 mg phosphorus daily. Log food sources and any supplements taken, noting the trimester of pregnancy.
  • Users can set daily reminders to consume calcium-rich foods or take supplements. The app could provide a list of high-calcium and high-phosphorus foods and suggest meal ideas that incorporate these nutrients. Users could log supplement use to ensure consistency, especially during the second and third trimesters.
  • Track mineral intake weekly and monthly to identify patterns. Create alerts if intake falls below recommended levels. Share reports with healthcare providers during prenatal visits. Monitor for any side effects from supplements and adjust as recommended by doctors.

This research suggests an association between mineral intake and premature birth risk but does not prove causation. These findings should not replace personalized medical advice from your obstetrician or healthcare provider. Every pregnancy is unique, and nutritional needs vary by individual. Before starting any new supplement regimen during pregnancy, consult with your doctor. This study was conducted in one geographic location and may not apply universally to all populations. If you have concerns about premature birth risk, discuss them with your healthcare provider who can assess your individual circumstances and provide tailored recommendations.