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 .
Effect of vitamin D3 supplementation in pregnancy on risk of pre-eclampsia - Randomized controlled trial.
BACKGROUND Vitamin D plays pivotal role in decidualization and implantation of the placenta . Recent research es have shown that low level of vitamin D3 " 25-hydroxyvitamin D ( 25[OH]D ) " in serum is a risk factor for pre-eclampsia . Latest evidence supports role of vitamin D3 deficiency treatment in reducing the risk of pre-eclampsia . The aim of this study is to determine the effect of antenatal supplementation of vitamin D3 on the risk of pre-eclampsia and to explore the dose effect in attaining the vitamin D3 normal level . METHOD An open labelled r and omized controlled study was conducted on 179 pregnant women presenting in King Fahad Medical City antenatal clinic from Oct 2012-Oct 2015 . Patients with age less than 20 years or more than 40 years , pregnancy with fetal anomalies , history of hypertension , pre-eclampsia , recurrent miscarriage , chronic renal or hepatic disease and malignancy were excluded from the study .  Serum 25[OH]D was analysed during the first trimester ( between 6 and 12 weeks of pregnancy ) . Patients with vitamin D3 deficiency ( serum levels < 25 nmol/L ) were included in the study and r and omized for vitamin D3 supplementation 400 IU ( Group 1 ) versus 4000 IU ( Group 2 ) . Both groups were compared for the prevalence of pre-eclampsia and dose effect on vitamin D level . RESULTS Of 179 gravidae enrolled , 164 completed the trial .  Mean maternal 25[OH]D was significantly increased in group 2 from 16.3 ± 5 nmol/mL to 72.3 ± 30.9 nmol/mL compared with group 1 from 17.5 ± 6.7 nmol/mL to 35.3 ± 20.7 nmol/mL ( p > 0.0001 ) . The relative risk reduction ( RRR ) for attaining ≥75 nmol/L before delivery was significantly higher ( RRR 93.2 [ CI 79 - 98 ] when treated with 4000 IU . The total incidence of pre-eclampsia in the study population was 4.3 % . In comparison to group 1 , the group 2 reported fewer pre-eclampsia events during the study period ( 8.6 % versus 1.2 % ; p < 0.05 ) . The total number of IUGRs was lesser in the group 2 ( 9.6 % ) versus group 1 ( 22.2 % ) ; p = 0.027 . However , other obstetric outcomes were comparable between both groups . CONCLUSION Vitamin D supplementation in the deficient group reduces the risk of pre-eclampsia and IUGR in a dose dependant manner . However larger clinical trials are essential to investigate optimum dosage of vitamin D3 in this group
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 .