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 .
Estimation of the maternal vitamin D intake that maintains circulating 25-hydroxyvitamin D in late gestation at a concentration sufficient to keep umbilical cord sera ≥25–30 nmol/L: a dose-response, double-blind, randomized placebo-controlled trial in pregnant women at northern latitude
ABSTRACT Background In the absence of dose-response data , Dietary Reference Values for vitamin D in nonpregnant adults are extended to pregnancy . Objective The aim was to estimate vitamin D intake needed to maintain maternal 25-hydroxyvitamin D [ 25(OH)D ] in late gestation at a concentration sufficient to prevent newborn 25(OH)D < 25–30 nmol/L , a threshold indicative of increased risk of nutritional rickets . Design We conducted a 3-arm , dose-response , double-blind , r and omized placebo-controlled trial in Cork , Irel and ( 51.9oN ) . A total of 144 white-skinned pregnant women were assigned to receive 0 , 10 ( 400 IU ) , or 20 ( 800 IU ) µg vitamin D3/d from ≤18 wk of gestation . Vitamin D metabolites at 14 , 24 , and 36 wk of gestation and in cord sera , including 25(OH)D3 , 3-epi-25(OH)D3 , 24,25(OH)2D3 , and 25(OH)D2 were quantified by liquid chromatography – t and em mass spectrometry . A curvilinear regression model predicted the total vitamin D intake ( from diet and antenatal supplements plus treatment dose ) that maintained maternal 25(OH)D in late gestation at a concentration sufficient to maintain cord 25(OH)D at ≥25–30 nmol/L. Results Mean ± SD baseline 25(OH)D was 54.9 ± 10.7 nmol/L. Total vitamin D intakes at the study endpoint ( 36 wk of gestation ) were 12.1 ± 8.0 , 21.9 ± 5.3 , and 33.7 ± 5.1 µg/d in the placebo and 10-µg and 20-µg vitamin D3 groups , respectively ; and 25(OH)D was 24.3 ± 5.8 and 29.2 ± 5.6 nmol/L higher in the 10- and 20-µg groups , respectively , compared with placebo ( P < 0.001 ) . For maternal 25(OH)D concentrations ≥50 nmol/L , 95 % of cord sera were ≥30 nmol/L and 99 % were > 25 nmol/L. The estimated vitamin D intake required to maintain serum 25(OH)D at ≥50 nmol/L in 97.5 % of women was 28.9 µg/d . Conclusions Thirty micrograms of vitamin D per day safely maintained serum 25(OH)D concentrations at ≥50 nmol/L in almost all white-skinned women during pregnancy at a northern latitude , which kept 25(OH)D at > 25 nmol/L in 99 % and ≥30 nmol/L in 95 % of umbilical cord sera . This trial was registered at www . clinical trials.gov as NCT02506439
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 .