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 .
Maternal gestational vitamin D supplementation and offspring bone health (MAVIDOS): a multicentre, double-blind, randomised placebo-controlled trial.
BACKGROUND Maternal vitamin D status has been associated with bone mass of offspring in many , but not all , observational studies . However , maternal vitamin D repletion during pregnancy has not yet been proven to improve offspring bone mass in a r and omised controlled trial . We aim ed to assess whether neonates born to mothers supplemented with vitamin D during pregnancy have greater whole-body bone mineral content ( BMC ) at birth than those of mothers who had not received supplementation . METHODS The Maternal Vitamin D Osteoporosis Study ( MAVIDOS ) was a multicentre , double-blind , r and omised , placebo-controlled trial that recruited pregnant women from three study sites in the UK ( Southampton , Oxford , and Sheffield ) . Eligible participants were older than 18 years , with a singleton pregnancy , gestation of less than 17 weeks , and a serum 25-hydroxyvitamin D ( 25[OH]D ) concentration of 25 - 100 nmol/L at 10 - 17 weeks ' gestation . P'articipants were r and omly assigned ( 1:1 ) , in r and omly permuted blocks of ten , to either cholecalciferol 1000 IU/day or matched placebo , taken orally , from 14 weeks ' gestation ( or as soon as possible before 17 weeks ' gestation if recruited later ) until delivery . Participants and the research team were masked to treatment allocation . The primary outcome was neonatal whole-body BMC , assessed within 2 weeks of birth by dual-energy x-ray absorptiometry ( DXA ) , analysed in all r and omly assigned neonates who had a usable DXA scan . Safety outcomes were assessed in all r and omly assigned participants . This trial is registered with the International St and ard R and omised Controlled Trial registry , IS RCT N 82927713 , and the European Clinical Trials Data base , EudraCT 2007 - 001716 - 23 . FINDINGS Between Oct 10 , 2008 , and Feb 11 , 2014 , we r and omly assigned 569 pregnant women to placebo  and 565 to cholecalciferol 1000 IU/day . 370 ( 65 % ) neonates in the placebo group and 367 ( 65 % ) neonates in the cholecalciferol group had a usable DXA scan and were analysed for the primary endpoint . Neonatal whole-body BMC of infants born to mothers assigned to cholecalciferol 1000 IU/day did not significantly differ from that of infants born to mothers assigned to placebo ( 61·6 g [ 95 % CI 60·3 - 62·8 ] vs 60·5 g [ 59·3 - 61·7 ] , respectively ; p=0·21 ) . We noted no significant differences in safety outcomes , apart from a greater proportion of women in the placebo group with severe post-partum haemorrhage than those in the cholecalciferol group ( 96 [ 17 % ] of 569 mothers in the placebo group vs 65 [ 12 % ] of 565 mothers in the cholecalciferol group ; p=0·01 ) . No adverse events were deemed to be treatment related . INTERPRETATION Supplementation of women with cholecalciferol 1000 IU/day during pregnancy did not lead to increased offspring whole-body BMC  compared with placebo , but did show that 1000 IU of cholecalciferol daily is sufficient to ensure that most pregnant women are vitamin D replete , and it is safe . These findings support current approaches to vitamin D supplementation in pregnancy . Results of the ongoing MAVIDOS childhood follow-up study are awaited . FUNDING Arthritis Research UK , Medical Research Council , Bupa Foundation , and National Institute for Health Research
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 .