Vitamin D has received lots of attention in recent years for its importance in a wide variety of illnesses affecting both children and adults. Its importance in pregnancy has also been widely established, affecting rates of gestational diabetes, pre-elcampsia, C-section, preterm births and post partum depression amongst others.
A recent paper was published highlighting the importance of Vitamin D not only throughout pregnancy, but more importantly, in the preconception period.
Now, there's some disagreement about what level of Vitamin D is enough for good health. Some groups advocate for levels of 50nmol/L being labelled as sufficient while others suggest levels need to be at least 75nmol/L or even 120nmol/L. It's important to know this when reading through scientific literature, as sometimes people are classified as being deficient or not, but which category they fall in to will depend on what benchmark is being used.
So, in the paper that was just done, they set "sufficiency" at equal to or greater than 75nmol/L, which is highly defensible, and perhaps even still too low. The question being examined was how maternal Vitamin D levels affect the rates of pregnancy and miscarriage.
Interestingly, it was found that women with sufficient levels of Vitamin D in the preconception period had higher rates of pregnancy and live birth than those with lower preconception levels. Perhaps more interestingly, this association did not hold when levels of Vitamin D were assessed at 8 weeks gestation (i.e. when she was 2 months pregnant, mom's vitamin D levels didn't seem to affect rates of miscarriage). So there was something about having enough Vitamin D either while her egg was developing or in the very very early stages of pregnancy that led to lower rates of miscarriage, that didn't have any effect later on in pregnancy (with regards to miscarrying).
This study is important and highlights what is perhaps true of many different vitamins, minerals and nutrients. Often, once a woman is pregnant, she begins to pay more serious attention to her diet and her health, but in some cases, it may be too late. This study reminds us that women's nutritional status before she conceives may play an even greater role in determining the outcome of her pregnancy in some respects.
Canadians are well known to be deficient in Vitamin D because of our latitude. In Alberta, we can't make Vitamin D the majority of the year. Supplementing is inexpensive and can make a huge difference in the health of mom and baby. Ideally, we would measure blood levels of all women before conception and adjust supplementation to ensure levels are high enough before trying to conceive. Sometimes this will mean delaying conception, but according to this study, the wait would be well worth it.
References
S.L. Mumford, R.A. Garbose, K. Kim et al." Association of preconception serum 25-hydroxyvitamin D concentrations with livebirth and pregnancy loss: a prospective cohort study." Lancet Diabetes Endocrinol. 2018.
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L. B. Andersen, J. S. Jorgensen, T. K. Jensen et al., “Vitamin D insufficiency is associated with increased risk of first-trimester miscarriage in the Odense Child Cohort,” The American Journal of Clinical Nutrition, vol. 102, no. 3, pp. 633–638, 2015.
S. L. Lau, J. E. Gunton, N. P. Athayde, K. Byth, and N. W. Cheung, “Serum 25-hydroxyvitamin D and glycated haemoglobin levels in women with gestational diabetes mellitus,” Medical Journal of Australia, vol. 194, no. 7, pp. 334–337, 2011.
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L. M. Bodnar, R. W. Platt, and H. N. Simhan, “Early-pregnancy vitamin D deficiency and risk of preterm birth subtypes,” Obstetrics & Gynecology, vol. 125, no. 2, pp. 439–447, 2015.
T. Zhu, T. J. Liu, X. Ge, J. Kong, L. J. Zhang, and Q. Zhao, “High prevalence of maternal vitamin D deficiency in preterm births in northeast China, Shenyang,” International Journal of Clinical and Experimental Pathology, vol. 8, no. 2, pp. 1459–1465, 2015.
A. Merewood, S. D. Mehta, T. C. Chen, H. Bauchner, and M. F. Holick, “Association between vitamin D deficiency and primary cesarean section,” The Journal of Clinical Endocrinology & Metabolism, vol. 94, no. 3, pp. 940–945, 2009.
Y.-H. Chen, L. Fu, J.-H. Hao et al., “Maternal vitamin D deficiency during pregnancy elevates the risks of small for gestational age and low birth weight infants in Chinese population,” The Journal of Clinical Endocrinology & Metabolism, vol. 100, no. 5, pp. 1912–1919, 2015.
C. W. Fu, J. T. Liu, W. J. Tu, J. Q. Yang, and Y. Cao, “Association between serum 25-hydroxyvitamin D levels measured 24 hours after delivery and postpartum depression,” BJOG: An International Journal of Obstetrics and Gynaecology, vol. 122, no. 12, pp. 1688–1694, 2015.