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 .
Association of preconception serum 25-hydroxyvitamin D concentrations with livebirth and pregnancy loss: a prospective cohort study.
BACKGROUND Vitamin D deficiency during pregnancy is associated with adverse pregnancy outcomes , although the association between preconception vitamin D concentrations and livebirth is unknown . We aim ed to assess the association between preconception vitamin D and pregnancy outcomes among women with proven fecundity . METHODS We did a secondary analysis of a prospect i ve cohort from the block-r and omised , double-blind , placebo-controlled EAGeR trial . Women aged 18 - 40 years with one to two previous pregnancy losses were recruited from June 15 , 2007 , to July 15 , 2011 , at four clinical sites in the USA and followed up for up to six menstrual cycles while attempting pregnancy and throughout pregnancy if they conceived . Serum 25-hydroxyvitamin D was measured at baseline ( preconception ) and 8 weeks of gestation . Outcomes of interest included clinical pregnancy , time to pregnancy , pregnancy loss , and livebirths . Risk ratios ( RRs ) and 95 % CIs for livebirths , pregnancy , and pregnancy loss were estimated with weighted log-binomial regression . To assess time to pregnancy , we used discrete time Cox proportional hazards models to calculate fecundability odds ratios ( FORs ) with 95 % CIs . EAGeR is registered with Clinical Trials.gov , number NCT00467363 . FINDINGS 1191 women had available data on preconception 25-hydroxyvitamin D concentrations . 555 ( 47 % ) women were classified as having sufficient concentrations ( ≥75 nmol/L ) and 636 ( 53 % ) as having insufficient concentrations ( < 75 nmol/L ) . Women with sufficient preconception 25-hydroxyvitamin D were more likely to achieve clinical pregnancy ( adjusted RR 1·10 [ 1·01 - 1·20 ] ) and livebirth ( 1·15 [ 95 % CI 1·02 - 1·29 ] ) than were women with insufficient concentrations . Among women who achieved pregnancy , sufficient preconception 25-hydroxyvitamin D , but not that at 8 weeks of gestation , was associated with reduced risk of pregnancy loss ( preconception RR per 25 nmol/L 0·88 [ 95 % CI 0·77 - 0·99 ] ; 8 weeks of gestation 0·98 [ 0·95 - 1·01 ] ) . No association was observed with fecundability in women with sufficient versus those with insufficient preconception 25-hydroxyvitamin D concentrations ( adjusted FOR 1·13 [ 95 % CI 0·95 - 1·34 ] ) . INTERPRETATION Sufficient preconception 25-hydroxyvitamin D ( ≥75 nmol/L ) was associated with increased likelihood of pregnancy and livebirth . Increased vitamin D concentrations before conception , but not in early pregnancy , were associated with reduced pregnancy loss . FUNDING National Institutes of Health and Doris Duke Charitable Foundation
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 .