A couple tries and tries to have a child, and then the magic moment happens: “Dear, I think I’m pregnant.” What a happy time (except for the morning sickness) as the couple looks forward to becoming parents. However, up to 20% of pregnant women lose their infant to a miscarriage.
Miscarriage is the most common adverse outcome of pregnancy. There are many causes of miscarriage, with environmental factors probably exceeding genetic factors in its causation. Identifying modifiable risk factors for miscarriage is potentially important for public health. A recent Danish study found that smoking, increased maternal age, alcohol consumption, pre-pregnancy obesity, heavy lifting, and nightshift work were important, preventable risk factors of miscarriage. About 80% of miscarriages occur in the first 12 weeks of pregnancy (the first trimester). The underlying mechanism in about half of the cases involve chromosomal abnormalities.
Some women struggle emotionally following a miscarriage. A questionnaire following a miscarriage showed that more than half (55%) presented with significant psychological distress immediately, while 25% did at 3 months; 18% showed psychological symptoms at 6 months and 11% at 1 year after the miscarriage. Besides the feeling of loss, a lack of understanding by others is often important. People who have not experienced it themselves may find it difficult to empathize with what has occurred, and how upsetting it may be. This may lead to unrealistic expectations of the parents’ recovery. The pregnancy and the miscarriage cease to be mentioned in conversations, often because the subject is too painful. This may make the woman feel particularly isolated. Interaction with pregnant women and newborn children may understandably be painful for parents who have experienced a miscarriage. Sometimes this makes interactions with friends, acquaintances and family very difficult.
However, there is a lot of test tube and animal studies indicating low vitamin D causes some miscarriages. When you think about it, getting pregnant is like having an organ transplant as the fetus is detected by the immune system as being a foreign invader. Activated vitamin D levels during the first few months of a pregnancy spikes up to three times the normal level, a condition that would cause dangerous high blood calcium in non-pregnant subjects. The spike in activated vitamin D, with its immune effects, is thought to be crucial in preventing the mother from rejecting the fetus.
Researchers in Denmark wanted to find if vitamin D levels had any discernable effect on miscarriage. They obtained vitamin D levels on 1,684 pregnant women early in the course of their pregnancy, and then followed them to see who had a miscarriage. Here is what they found:
- Women who had miscarriages had lower vitamin D levels, 55.6 nmol/L (22 ng/ml) than women who did not miscarry 66 nmol/L (26 ng/ml) (P=.002).
- Women with levels less than 50 nmol/l (20 ng/ml) were 2.5 times more likely to have a miscarriage than women with levels above 50 nmol/L (20 ng/ml) (P<.05).
- The effect was only seen in first trimester miscarriages; the trend in second trimester miscarriages just missed statistical significance.
The researchers concluded,
“In conclusion, we found an association between 25(OH)D concentrations and first-trimester miscarriage, indicating that vitamin D concentrations, 50 nmol/L (20 ng/ml) in the first trimester were associated with a 2.5 times higher risk for a subsequent first-trimester miscarriage. These findings suggest a protective role for vitamin D against miscarriage. To test this hypothesis, randomized controlled trials should be performed to investigate the possible effect of increasing 25(OH)D concentrations by supplementation in early pregnancy or even pre-conceptually.”
However, in order to do a randomized placebo controlled trial the placebo group would have to have low vitamin D levels throughout pregnancy. Given what we know about vitamin D’s role in growth and development of the fetus, as well as adverse pregnancy outcomes associated with low vitamin D, such as preeclampsia or premature infancy, how can researchers ethically conduct such a study?