Researchers studied nearly 7,000 pregnant women in New Zealand to understand why some babies are born too early (before 37 weeks). They looked at what mothers ate, whether they took vitamins, where they lived, and other life factors. The study found that eating too much junk food, not taking iron supplements in later pregnancy, and living in certain rural areas were linked to earlier births. Interestingly, many factors doctors usually worry about—like a mother’s age or weight—didn’t seem to matter as much in this group. The findings suggest that improving nutrition during pregnancy, especially iron intake, might help babies stay in the womb longer.

The Quick Take

  • What they studied: What things in a pregnant woman’s life and diet are connected to babies being born early (before 37 weeks of pregnancy)
  • Who participated: 6,822 pregnant women in New Zealand who had babies between 2009 and 2010. The study looked at their health records, what they ate, and where they lived.
  • Key finding: About 1 in 15 babies (6.6%) were born early. Eating lots of junk food made early birth 28% more likely, and not taking iron supplements in the second half of pregnancy made it 46% more likely. Living in certain rural areas also increased the risk.
  • What it means for you: If you’re pregnant or planning to be, focusing on healthy eating and taking iron supplements as recommended may help reduce the chance of early birth. However, this study shows connections, not proof that these factors cause early birth.

The Research Details

This was a cohort study, which means researchers followed a large group of women over time and collected information about their lives, diets, and pregnancies. The researchers used data that was already collected from 6,822 New Zealand mothers between 2009 and 2010. They looked back at this information to see which factors were connected to babies being born early.

The researchers asked mothers about what they ate, whether they took vitamins and supplements, where they lived, and details about their age, weight, and background. They used special computer programs to analyze all this information and look for patterns. They used a method called ‘multilevel modeling’ which helps account for the fact that some neighborhoods or areas might have different rates of early birth.

This approach is important because early birth is a serious health problem that affects many babies. By studying a real group of mothers and their actual pregnancies, researchers can find real-world connections between everyday factors (like diet) and early birth. This is better than just studying one small group or doing an experiment, because it shows what actually happens in people’s lives.

This study is fairly reliable because it included a large number of women (nearly 7,000) and used careful statistical methods. The researchers looked at many different factors at once. However, because they looked back at information that was already collected, they couldn’t prove that diet or supplements directly caused the differences in early birth—only that they were connected. The study was done in New Zealand, so the results might be slightly different in other countries with different populations.

What the Results Show

The study found that 436 babies out of 6,667 births (about 6.6%) were born early. Surprisingly, many factors that doctors often worry about—like the mother’s age, how many children she’d had before, her weight, her ethnicity, or how poor her neighborhood was—were NOT significantly connected to early birth in this group.

However, three things WERE connected to higher chances of early birth: First, eating a ‘junk food’ diet (lots of processed foods, sugary drinks, and unhealthy snacks) made early birth 28% more likely. Second, not taking iron supplements after the first three months of pregnancy made early birth 46% more likely. Third, living in rural areas that had some urban influence (not completely rural, but not fully urban either) made early birth 2.4 times more likely.

Interestingly, not following the government’s guidelines about bread and cereal actually seemed to reduce the risk of early birth slightly, though researchers aren’t sure why this happened.

The study also measured something called the ‘Healthy Location Index,’ which rates how healthy an area is based on things like access to parks, shops, and services. This measure didn’t show a clear connection to early birth, even though researchers expected it might. This suggests that where you live matters less than what you eat and what supplements you take.

Previous research has shown that nutrition and supplements are important during pregnancy, and this study supports that. However, this study is interesting because it found that some traditional risk factors (like mother’s age and weight) weren’t as important in this particular group of New Zealand women. This might mean that in developed countries with good healthcare, these factors matter less than diet and supplements.

This study has some important limits. First, it only looked at women in New Zealand, so the results might be different in other countries. Second, the researchers couldn’t prove that junk food or missing iron supplements actually caused early birth—only that they were connected. Third, the study relied on mothers remembering what they ate and whether they took supplements, which might not be perfectly accurate. Fourth, the study couldn’t look at all possible factors that might affect early birth, so there might be other important things they missed.

The Bottom Line

Pregnant women should aim to eat a balanced diet with plenty of whole grains, fruits, vegetables, and proteins, and limit junk food and processed snacks (moderate confidence). Taking iron supplements as recommended by your doctor, especially in the second and third trimesters, appears important (moderate confidence). These changes are safe and recommended by health organizations anyway, so they’re worth doing. However, this study shows connections, not definite proof, so these changes should be part of overall prenatal care, not a replacement for it.

This information is most relevant for pregnant women or women planning to become pregnant. It’s also useful for doctors, midwives, and public health workers who help pregnant women. Women living in rural areas might especially benefit from paying attention to nutrition. However, if you have specific pregnancy concerns or risk factors, talk to your doctor rather than relying only on this study.

Good nutrition and iron supplements work throughout pregnancy, but they’re especially important in the second and third trimesters (after the first three months). You wouldn’t see immediate changes, but following these guidelines throughout pregnancy may help reduce the risk of early birth. Benefits would be measured in weeks of pregnancy, not days.

Want to Apply This Research?

  • Track daily iron supplement intake (yes/no) and rate daily diet quality on a simple scale (1=mostly junk food, 5=mostly healthy whole foods). Monitor these weekly to ensure consistency, especially after the first trimester of pregnancy.
  • Set a daily reminder to take iron supplements after the first trimester. Use the app to log meals and get feedback on whether your diet is balanced or too heavy on processed foods. Set a goal to reduce junk food servings per week.
  • Create a weekly nutrition scorecard that tracks: iron supplement adherence (target: 100%), junk food servings (target: fewer than 3 per week), and whole grain/fruit/vegetable servings (target: at least 5 per day). Share results with your healthcare provider at prenatal visits.

This research shows connections between diet, supplements, and early birth, but does not prove cause and effect. Preterm birth has many complex causes, and this study cannot account for all of them. This information should not replace medical advice from your doctor or midwife. If you are pregnant or planning to become pregnant, discuss nutrition, supplements, and any concerns about early birth risk with your healthcare provider. Every pregnancy is different, and your doctor can give you personalized advice based on your individual health situation.