During pregnancy, maternal and fetal Ca demands are met through increased
intestinal Ca absorption. Increased Ca absorption may be more dependent on
oestrogen's up-regulation of Ca transport genes than on vitamin D
status. Numerous studies, however, have found that severe vitamin D deficiency
with secondary hyperparathyroidism during pregnancy leads to abnormal Ca
homoeostasis in the neonate. Some, but not all, studies of maternal vitamin D
supplementation during pregnancy find a greater birth weight among infants of
mothers with adequate vitamin D status. Observational studies find a higher
incidence of small-for-gestational age (SGA) infants among
mothers who are vitamin D deficient, but this effect may be modified by
genetics. In addition, the effect of vitamin D status on SGA may not be linear,
with increased occurrence of SGA at high maternal 25-hydroxyvitamin D
(25-OHD) concentrations. Some studies, but not all, also
have found that maternal vitamin D status is associated with growth trajectory
during the first year of life, although the findings are contradictory. There
are recent studies that suggest maternal 25-OHD, or surrogates of vitamin D
status, are associated with growth and bone mass later in childhood. These
results are not consistent, and blinded randomised trials of vitamin D
supplementation during pregnancy with long-term follow-up are needed to
determine the benefits, and possible risks, of maternal vitamin D status on
offspring growth and bone development. The possibility of adverse outcomes with
higher maternal 25-OHD concentrations should be considered and investigated in
all ongoing and future studies.