With so many things to think about during pregnancy, it can be difficult for expectant mothers to keep up, particularly with the latest advice on how to stay healthy. Health professionals can also face challenges in giving their pregnant patients the best advice, in light of emerging research.

Vitamin D is one such complex area, with data from a 2012 study of Australians aged 25+ finding that vitamin D deficiency affects 39% of Australian women.1

Vitamin D deficiency in pregnancy has been linked to several conditions including high blood pressure and preeclampsia in expectant mothers, and low calcium levels, rickets and myopathy (muscle disease) in newborns.

An Adelaide team of pathologists led by chemical pathologist Dr Devika Thomas, collated test results over a 12-month period, from blood samples of pregnant women who were referred for a vitamin D test by their doctor.

This data, collected in 2018, was presented at the Australian Association of Clinical Biochemists’ Annual Scientific Conference earlier this month and shows a third of pregnant women in South Australia are vitamin D deficient.

Current guidelines state that only women deemed high risk should have vitamin D levels tested. This includes women with darker skin such as those from Aboriginal, African or South Asian backgrounds, newly arrived refugees, and those whose sun exposure is severely limited, including veiled women.

However, it can be difficult for health professionals looking after pregnant women to know when a woman might be at risk of low vitamin D. Low levels are relatively common in the general population, plus there are many factors affecting sun exposure and vitamin D absorption, including the seasonal and geographical differences.

Dr Thomas says the issue is particularly important for pregnant women:

“Vitamin D deficiency is not uncommon in the general population in Australia but current guidelines for testing in pregnancy cover a limited group of women. We wanted to find out if vitamin D deficiency is identified and corrected during pregnancy. We found that 22% of the women tested at 28 weeks as per guidelines are still deficient.”

Of the 1,352 pathology referrals that were included in the study, there were only 575 that included a request for vitamin D testing. This equates to 43 per cent which is consistent with the proportion of women deemed high-risk in previous studies using comparable demographics.

Current South Australian guidelines recommend that low-risk women should take daily supplements containing 400IU of vitamin D.

Women deemed at high risk of deficiency should be tested at their first antenatal visit and begin taking daily supplements containing 1000IU of vitamin D.

For these women, test results should be checked at the next appointment and dosage reduced if levels are adequate.

Women still found to have low vitamin D levels will continue on higher dose supplements and be tested again at 28 weeks. These results will determine if supplements need to be further increased.

Dr Thomas said, “This approach does not detect and treat all pregnant women who are deficient in vitamin D. The criteria for testing rely on some self-reported data and people may overestimate their sun exposure.

“Although we saw a slight rise in the rates of adequate vitamin D levels in the third trimester, this was not statistically significant, therefore even in those who were deemed high-risk and tested in the first trimester, the majority are still deficient by the third trimester.”

Vitamin D in the mother’s blood needs to be up to the recommended level by week 28 of pregnancy in order for a baby to be born with an adequate level of stored vitamin D.

In other states the approach may be different with some guidelines stating supplementation should not be routinely recommended to all pregnant women, only those tested and found to have low vitamin D levels. This could also create some confusion for patients and their health professionals and points to a need for more research on vitamin D.

“I think further research in this area is needed to determine if offering testing to all women in early pregnancy could detect and treat more women with vitamin D deficiency. Studies looking at adherence to supplements and investigating the optimum level of vitamin D in pregnancy could also help to provide the best outcomes for mothers and babies,” said Dr Thomas.

A/Prof Graham Jones is a chemical pathologist and an ambassador for Pathology Awareness Australia. He pointed out the importance of communication between patients, clinicians and pathology teams:

“During pregnancy women have a lot of pathology tests to monitor their health and the health of their baby. As part of this process they will need to answer questions about medical and family history, lifestyle, diet and medications – including any supplements – to ensure that their treating doctors have all the information they need to order the appropriate tests. This information is also very important for pathology laboratories when interpreting results.

“Vitamin D testing is a particularly complex area with seasonal fluctuations and several factors which can affect whether a woman is at high risk of deficiency. Pregnant women should discuss with their doctor or midwife if testing is appropriate.”

There always needs to be a clinical reason for a doctor to request a test whether vitamin D or anything else – so if in doubt, ask your doctor.


  1. Daly RM et al. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clin Endocrinol 2012. Access: https://www.ncbi.nlm.nih.gov/pubmed/22168576