Vitamin D plays an important role in promoting healthy pregnancy and fetal development. There is a lack of knowledge on (1) the effect of vitamin D deficiency/ insufficiency on pregnancy and neonatal outcomes, (2) the association between maternal plasma vitamin D concentration and dietary intake, and (3) the prevalence of vitamin D deficiency/ insufficiency during pregnancy and the contribution of vitamin D metabolites to estimate vitamin D. This dissertation attempts to address these knowledge gaps about vitamin D during pregnancy.
In a systematic review and meta-analysis of observational studies, low maternal 25(OH)D concentrations were found to be associated with higher risks of gestational diabetes (pooled OR 1.49, 95% CI: 1.18 to 1.89), preeclampsia (pooled OR 1.79, 95% CI: 1.25 to 2.58), small for gestational age (SGA) (pooled OR 1.85, 95% CI: 1.52 to 2.26) and lower birth weight (weighted mean difference: -130.92 g (95% CI: -186.69 to -75.14). However, that quality of individual studies was not always optimal due to inconsistent reporting on confounding factors.
The two studies in this work involved pregnant women from a large Alberta cohort study to measure vitamin D. 3-epi-25(OH)D3 was found in all of the pregnant women’s blood in mid-pregnancy, at the time of delivery and in cord blood. When the 3-epimer was included in the estimation of status, the prevalence of vitamin D <75 nmol/L was significantly lower (P<0.005). A significant relationship between maternal reported dietary vitamin D intake and plasma 25(OH)D and 3-epi-25(OH)D3 concentration were identified. Consuming the Recommended Dietary Allowance (RDA) (600 IU/ day) was found to be insufficient to achieve vitamin D <75 nmol/L in half of participants.
This research highlighted the potentially important association between maternal vitamin D status and pregnancy health and the variability that can arise in study results when different measures of vitamin D status are used. In addition, it extends the literature suggesting that current RDA may not be adequate to ensure that Canadian pregnant women achieving vitamin D status. Furthermore, this research showed that the method employed to measure vitamin D in pregnant women and cord blood can influence the estimates of status.