Meta-analyses of r and omized controlled trials ( RCTs ) document that physiological vitamin D supplementation during pregnancy is safe and improves vitamin D and calcium status , thereby protecting skeletal health .
Although certain RCTs and /or meta-analyses reported some other beneficial effects , it is still not clear whether vitamin D supplementation  improves fertility or decreases the risk of adverse pregnancy outcomes such as low birth weight , pre-eclampsia and neonatal mortality , or reduces wheeze/asthma in the infants .
Vitamin D deficiency is common and there exists a huge gap between recommended dietary vitamin D intakes and the poor vitamin D supply in the general population .
While vitamin D is important for musculoskeletal health , there are accumulating data suggesting that vitamin D may also be important for fertility , pregnancy outcomes and lactation .
Significant changes in vitamin D metabolism during pregnancy such as increased production of the " active vitamin D hormone " calcitriol support the important role of vitamin D in this setting .
Observational studies show that vitamin D deficiency is a risk marker for reduced fertility and various adverse pregnancy outcomes and is associated with a low vitamin D content of breast milk .
Nevertheless , vitamin D supplementation in pregnant women is frequently required to achieve a sufficient vitamin D status as recommended by nutritional vitamin D guidelines .
Vitamin D supplementation during pregnancy: double-blind, randomized clinical trial of safety and effectiveness.
The need , safety , and effectiveness of vitamin D supplementation during pregnancy remain controversial . In this r and omized , controlled trial , women with a singleton pregnancy at 12 to 16 weeks ' gestation received 400 , 2000 , or 4000 IU of vitamin D(3 ) per day until delivery . The primary outcome was maternal/neonatal circulating 25-hydroxyvitamin D [ 25(OH)D ] concentration at delivery , with secondary outcomes of a 25(OH)D concentration of 80 nmol/L or greater achieved and the 25(OH)D concentration required to achieve maximal 1,25-dihydroxyvitamin D(3 ) [ 1,25(OH)(2)D(3 ) ] production . Of the 494 women enrolled , 350 women continued until delivery : Mean 25(OH)D concentrations by group at delivery and 1 month before delivery were significantly different ( p < 0.0001 ) , and the percent who achieved sufficiency was significantly different by group , greatest in 4000-IU group ( p < 0.0001 ) . The relative risk ( RR ) for achieving a concentration of 80 nmol/L or greater within 1 month of delivery was significantly different between the 2000- and the 400-IU groups ( RR = 1.52 , 95 % CI 1.24 - 1.86 ) , the 4000- and the 400-IU groups ( RR = 1.60 , 95 % CI 1.32 - 1.95 ) but not between the 4000- and . 2000-IU groups ( RR = 1.06 , 95 % CI 0.93 - 1.19 ) . Circulating 25(OH)D had a direct influence on circulating 1,25(OH)(2)D(3 ) concentrations throughout pregnancy ( p < 0.0001 ) , with maximal production of 1,25(OH)(2)D(3 ) in all strata in the 4000-IU group . There were no differences between groups on any safety measure . Not a single adverse event was attributed to vitamin D supplementation or circulating 25(OH)D levels . It is concluded that vitamin D supplementation of 4000 IU/d for pregnant women is safe and most effective in achieving sufficiency in all women and their neonates regardless of race , whereas the current estimated average requirement is comparatively ineffective at achieving adequate circulating 25(OH)D concentrations , especially in African Americans
Meta-analyses of r and omized controlled trials ( RCTs ) document that physiological vitamin D supplementation during pregnancy is safe and improves vitamin D and calcium status , thereby protecting skeletal health .
Although certain RCTs and /or meta-analyses reported some other beneficial effects , it is still not clear whether vitamin D supplementation  improves fertility or decreases the risk of adverse pregnancy outcomes such as low birth weight , pre-eclampsia and neonatal mortality , or reduces wheeze/asthma in the infants .
Vitamin D deficiency is common and there exists a huge gap between recommended dietary vitamin D intakes and the poor vitamin D supply in the general population .
While vitamin D is important for musculoskeletal health , there are accumulating data suggesting that vitamin D may also be important for fertility , pregnancy outcomes and lactation .
Significant changes in vitamin D metabolism during pregnancy such as increased production of the " active vitamin D hormone " calcitriol support the important role of vitamin D in this setting .
Observational studies show that vitamin D deficiency is a risk marker for reduced fertility and various adverse pregnancy outcomes and is associated with a low vitamin D content of breast milk .
Nevertheless , vitamin D supplementation in pregnant women is frequently required to achieve a sufficient vitamin D status as recommended by nutritional vitamin D guidelines .