The review found no eligible studies for this question.
Vitamin D + calcium supplementation may leads to higher preterm birth (less than 37 weeks' gestation) compared with placebo or no intervention (low certainty).
It is very uncertain whether vitamin D + calcium supplementation changes low birthweight (less than 2500 g) compared with placebo or no intervention (very low certainty).
Vitamin D + calcium supplementation probably leads to lower pre‐eclampsia compared with placebo or no intervention (moderate certainty).
It is very uncertain whether vitamin D + calcium supplementation changes gestational diabetes compared with placebo or no intervention (very low certainty).
It is very uncertain whether wheat flour or wheat flour products fortified with folic acid plus… changes spina bifida compared with unfortified wheat flours or wheat flour products (not containing… (very low certainty).
It is very uncertain whether wheat flour or wheat flour products fortified with folic acid plus… changes encephalocoele compared with unfortified wheat flours or wheat flour products (not containing… (very low certainty).
It is very uncertain whether wheat flour or wheat flour products fortified with folic acid plus… changes fatal anencephaly compared with unfortified wheat flours or wheat flour products (not containing… (very low certainty).
It is very uncertain whether wheat flour or wheat flour products fortified with folic acid plus… changes anaemia compared with unfortified wheat flours or wheat flour products (not containing… (very low certainty).
Wheat flour or wheat flour products fortified with folic acid plus… showed no clear difference in anaemia compared with unfortified wheat flours or wheat flour products (not containing… (low certainty).
It is very uncertain whether wheat flour or wheat flour products fortified with folic acid plus… changes neural tube defects (spina bifida, encephalocoele, anencephaly‐fatal… compared with unfortified wheat flours or wheat flour products (not containing… (very low certainty).
A dose of vitamin D 601 IU or higher showed no clear difference in pre‐eclampsia compared with 600 IU or lower alone or with other nutrients (low certainty).
A dose of vitamin D 601 IU or higher probably leads to lower gestational diabetes compared with 600 IU or lower alone or with other nutrients (moderate certainty).
A dose of vitamin D 601 IU or higher showed no clear difference in preterm birth compared with 600 IU or lower alone or with other nutrients (low certainty).
It is very uncertain whether A dose of vitamin D 601 IU or higher changes low birthweight compared with 600 IU or lower alone or with other nutrients (very low certainty).
Summary of findings table ‐ Vitamin D showed no clear difference in proportion of participants with one or more exacerbations treated… compared with placebo (high certainty).