It's estimated that 30 to 40 per cent of all conceptions result in a pregnancy loss before the 20-week mark. That number may seem high, but that's because many miscarriages happen before a woman even knows she's pregnant.
While the causes of many miscarriages remain a mystery, a recent study has linked a lack of vitamin D to a higher chance of pregnancy loss. Researchers from the US National Institutes of Health (NIH) followed women who had already suffered a pregnancy loss and found that those with lower levels of vitamin D took longer to get pregnant, and may have had an elevated risk of miscarriage.
"Our findings suggest that vitamin D may play a protective role in pregnancy," said Dr Sunni Mumford, the study's lead researcher.
Women with enough vitamin D were 10 per cent more likely to get pregnant, and 15 per cent more likely to have a live birth, according to the NIH. Also, with each additional 10 nanogram per millilitre increase in vitamin D before conception, there was a 12 per cent lower risk of pregnancy loss.
At this stage there is no evidence that the vitamin D deficiency was the direct cause of these results, but it does suggest a link, says Melbourne obstetrician and spokesperson for the Royal Australian and New Zealand College of Obstetricians and Gynaecologists Dr Philippa Costley.
"This article is not conclusive in linking vitamin D deficiency with miscarriage," she says. "Further studies are required.
"The exact dose required to maintain this level varies from person to person as the majority of vitamin D is produced when ultraviolet rays from sunlight strike the skin and trigger this," says Dr Costley. "For this reason, all women absorb different amounts of vitamin D depending on their skin type and sun exposure."
Vitamin D deficiency is on the rise, says Dr Costley, for the understandable reason that many women are conscious of being sun-smart and limiting direct sun exposure. She says the easiest way to check whether you have adequate levels of vitamin D is by asking your doctor for a blood test.
"This is extremely important if you have added risk factors such as dark skin, limited sun exposure due to an indoor lifestyle, or wear clothing covering the majority of your skin at all times," says Dr Costley.
The main vitamin D source is the sun, but there is also a small amount in some foods such as egg yolks, salmon and cod liver oil. Some foods are also fortified with vitamin D such as milk – plus it is also included in most pregnancy multivitamins.
Dr Costley says if your blood test shows a vitamin D deficiency, your doctor will usually give you a supplement to build your levels.