Researchers studied 111 women with PCOS (a common condition affecting fertility) who were trying to get pregnant using IVF or ICSI treatments. They measured vitamin D levels in the women’s blood before the embryo was placed in the uterus. Women who got pregnant had higher vitamin D levels than those who didn’t. The study found that women with vitamin D levels above a certain threshold were more likely to become pregnant and have successful births. This suggests that vitamin D might be an important factor in fertility treatment success, and taking vitamin D supplements before treatment might help improve outcomes.

The Quick Take

  • What they studied: Whether vitamin D levels in a woman’s blood affect the chances of getting pregnant and having a successful birth when using IVF or similar fertility treatments
  • Who participated: 111 women with PCOS (polycystic ovary syndrome, a hormone condition that can make getting pregnant harder) who received fertility treatment at a hospital in China between January 2022 and October 2024
  • Key finding: Women who became pregnant had significantly higher vitamin D levels (65.28 nmol/L) compared to women who didn’t get pregnant (52.22 nmol/L). Women with vitamin D levels above 67.95 nmol/L had a 75% chance of having a successful birth, while those below this level had only a 52% chance.
  • What it means for you: If you have PCOS and are considering fertility treatment, maintaining healthy vitamin D levels before treatment may improve your chances of success. However, this is one study with a relatively small group, so talk to your doctor about whether vitamin D supplementation is right for you before starting treatment.

The Research Details

This was a cohort study, which means researchers followed a group of women over time and tracked what happened to them. The researchers enrolled 111 women with PCOS who were undergoing IVF (in vitro fertilization, where eggs are fertilized in a lab) or ICSI (a similar procedure where sperm is injected directly into an egg). Before the embryo was transferred into the uterus, the researchers measured each woman’s vitamin D level in her blood. They then followed these women to see who became pregnant, who had successful births, and who had early miscarriages.

The researchers used statistical methods to analyze the data, including something called logistic regression, which helps determine whether vitamin D levels were truly connected to pregnancy success even when accounting for other factors like age, weight, and hormone levels. They also used ROC curve analysis to find the best vitamin D level that predicted pregnancy success.

This research approach is important because it looks at real women going through actual fertility treatment, rather than just studying cells in a lab. By measuring vitamin D before treatment and then tracking outcomes, the researchers could see if there was a real connection between vitamin D and success. The statistical methods they used help ensure that the connection between vitamin D and pregnancy wasn’t just due to chance or other factors.

This study has some strengths: it measured vitamin D at a specific, important time (before embryo transfer), it tracked important outcomes (pregnancy and live birth), and it adjusted for other factors that might affect results. However, the study is relatively small (111 women), was conducted at a single hospital in China, and is observational rather than experimental. This means we can see that vitamin D and pregnancy success are connected, but we can’t be completely certain that vitamin D causes better outcomes. The results need to be confirmed in larger studies before making strong recommendations.

What the Results Show

Out of 111 women in the study, 76 (about 68%) became pregnant. These pregnant women had significantly higher vitamin D levels before treatment compared to the 35 women who didn’t become pregnant. Specifically, pregnant women averaged 65.28 nmol/L of vitamin D, while non-pregnant women averaged 52.22 nmol/L—a meaningful difference.

When researchers looked at which vitamin D level best predicted pregnancy success, they found that 67.95 nmol/L was the optimal cutoff point. Women with vitamin D levels at or above this threshold had much better outcomes: 75% had successful live births, compared to only 52% of women with lower vitamin D levels.

Among the women who did become pregnant, those who had successful live births maintained higher vitamin D levels (67.63 nmol/L) than those who had early miscarriages (58.22 nmol/L). This suggests that vitamin D may not only help with getting pregnant but also with maintaining pregnancy.

The study found that even after accounting for other important factors like age, weight, and hormone levels (including LH, a key fertility hormone), vitamin D remained significantly associated with pregnancy success. This suggests that vitamin D’s connection to fertility outcomes is independent of these other factors. The high specificity (94.3%) of the vitamin D cutoff means that if a woman has vitamin D levels above 67.95 nmol/L, it’s very likely she’s in a group with better pregnancy outcomes.

Previous research has suggested that vitamin D plays a role in fertility and reproductive health, but its specific impact on women with PCOS undergoing IVF hasn’t been thoroughly studied. This research adds important evidence that vitamin D may be particularly relevant for this specific group of women. The findings align with other studies showing that vitamin D supports reproductive function, though more research is needed to confirm these results in different populations.

This study has several important limitations to keep in mind. First, it’s relatively small with only 111 women, all treated at one hospital in China, so results may not apply to all women with PCOS everywhere. Second, the study is observational, meaning researchers watched what happened naturally rather than randomly assigning women to receive vitamin D or a placebo—this means we can’t be certain that vitamin D directly causes better outcomes. Third, the study doesn’t tell us the best way to supplement vitamin D or when to start supplementation. Finally, the study didn’t measure vitamin D levels at other important times, only before embryo transfer, so we don’t know if vitamin D levels at other stages matter.

The Bottom Line

Based on this research, women with PCOS who are planning fertility treatment may want to discuss vitamin D supplementation with their doctor. The evidence suggests that maintaining vitamin D levels above 67.95 nmol/L (or about 27 ng/mL in other units) may improve chances of pregnancy and successful birth. However, this recommendation comes with moderate confidence because it’s based on one study with a limited number of participants. More research is needed before making strong, universal recommendations. Your doctor can test your vitamin D level and recommend appropriate supplementation based on your individual situation.

This research is most relevant to women with PCOS who are considering or undergoing IVF or ICSI treatment. Women with PCOS who are trying to conceive naturally might also benefit from maintaining healthy vitamin D levels, though this study doesn’t directly address that. Men and women without PCOS may have different vitamin D needs and fertility outcomes. Anyone considering vitamin D supplementation should consult with their healthcare provider, especially if they have kidney disease, take certain medications, or have other health conditions.

If you start vitamin D supplementation, it typically takes several weeks to months to build up adequate levels in your body. Most fertility specialists recommend optimizing vitamin D levels before starting fertility treatment, ideally 2-3 months in advance. However, if you’re already in treatment, it’s still worth discussing with your doctor whether supplementation might help. Don’t expect immediate results—vitamin D works gradually to support your body’s reproductive function.

Want to Apply This Research?

  • Track your vitamin D supplementation dose and timing daily, and log your vitamin D blood test results when available. Note the date of any blood tests and the measured vitamin D level (in nmol/L or ng/mL). If you’re undergoing fertility treatment, correlate your vitamin D levels with treatment milestones like egg retrieval and embryo transfer dates.
  • If your doctor recommends vitamin D supplementation, set a daily reminder to take your supplement at the same time each day (vitamin D is fat-soluble and best absorbed with a meal containing fat). Use the app to track consistency and set a goal of 90%+ adherence. Also log sun exposure time when possible, as sunlight helps your body produce vitamin D naturally.
  • Schedule vitamin D blood tests at key points: before starting fertility treatment, 8-12 weeks after starting supplementation, and before embryo transfer. Use the app to set reminders for these tests and track results over time. If you’re not seeing improvements in vitamin D levels after 12 weeks of supplementation, discuss with your doctor whether your dose needs adjustment or if absorption issues might be present.

This research summary is for educational purposes only and should not replace professional medical advice. The findings are based on a single observational study and should not be considered definitive medical guidance. Women with PCOS considering fertility treatment should consult with their reproductive endocrinologist or fertility specialist before starting any vitamin D supplementation or making changes to their treatment plan. Individual vitamin D needs vary based on age, location, skin tone, diet, and other health factors. Blood tests should be performed to determine your actual vitamin D status before supplementation. This summary does not constitute medical advice, diagnosis, or treatment recommendations.