Limitations of this study
PREGNANCY COMPLICATIONS, VITAMIN D DEFICIENCY, RECRUITMENT, EARLY PREGNANCY
A key limitation was the exclusion of women with 25(OH)D < 25 nmol/l in early pregnancy due to ethical and governance issues. Further intervention studies are, therefore, required in women with vitamin D deficiency who might particularly benefit from supplementation. Over 95% of the MAVIDOS participants were of White ethnicity, which reflects the local populations from which recruitment occurred but limits the generalisability of the study findings. Data on clothing choices, UVB exposure, dietary intake of vitamin D and previous pregnancy complications and outcomes were not collected. Nonetheless, considering the randomised controlled trial design of the study and inclusion of all women in the outcomes assessed in these analyses, random distribution of these characteristics between the two groups would be expected. These post hoc analyses are hypothesis-generating, rather than part of the pre-specified analysis plan for MAVIDOS, which primarily aimed to assess the effect of antenatal cholecalciferol supplementation on offspring bone development.