vitamin d is a fat - soluble vitamin obtained by the human body in two possible ways .
there can be a dietary intake , mainly through fatty fish , eggs and fortified food as well as endogenous production , where transformation of 7-dehydrocholesterol into vitamin d in the skin occurs after exposure to ultraviolet b radiation . in the liver , vitamin d
is hydroxylated to 25-hydroxyvitamin d. subsequent hydroxylation in the kidney forms the active metabolite , 1,25-oh vitamin d. in pregnancy , there is a 2-fold higher concentration of 1,25-oh vitamin d in maternal serum due to activity of placental 1--hydroxylase ( novakovic et al . , 2009 ) .
vitamin d not only influences bone mineralisation but has implications on maternal and fetal well - being .
25-oh vitamin d deficiency is associated with an increased risk of developing preeclampsia ( bodnar et al . , 2007 ; haugen et al . , 2009 ) , multiple sclerosis ( hayes et al . , 1997 ; pierrot - deseilligny , 2009 ) and schizophrenia ( mcgrath , 1999 ; mcgrath et al . ,
there is also an association with type 1 diabetes ( stene et al . , 2000 ) and asthma ( brehm et al . , 2009 ; erkkola et al . , 2009 ; willers et al . , 2007 ) after deficiency in utero or in early life .
neonates from deficient mothers have lower birthweight ( mannion et al . , 2006 ; sabour et al . , 2006 ; scholl and chen , 2009 ) and at age 9 still demonstrate a lower bone mineral content ( javaid et al . ,
2006 ) . in vitro studies have suggested a protective effect of 25-oh vitamin d against malignancies such as breastcancer and cancer of the colon .
risk factors for developing deficiency have been identified ; living in northern latitudes , limited sun exposure , dark skin , poor social circumstances and extensive clothing are amongst the most common ones ( baile et al . , 1979 ;
, 2009 ; mulligan et al . , 2009 ; sachan et al . , 2005 ;
, 2009 ; taha et al . , 1984 ; waiters et al . , 1999 ;
this makes immigrants in northern countries , especially when dark skinned and/or covered , extremely vulnerable ( bowyer et al . , 2009 ;
, 2006 ; wielders et al . , 2006 ) ( clemens et al . , 1982 ) .
results of vitamin d status in the pregnant flemish population have never been published before .
this pilot study aims at determining the prevalence of vitamin d deficiency in the antwerp population .
the pilot study ran from august 1 , 2009 until november 30 , 2009 after approval of the local ethical commitee was obtained . in each blood sample that was taken from pregnant women consulting the antenatal clinic , we determined 25-oh vitamin d. the nurse taking the blood samples put every patient in a category according to their sun exposure .
there were three possible categories : not covered , covering of only the head and leaving arms exposed to sun or complete covering with no sun exposure except for the face .
because part of the period studied coincided with the month ramadan , we also asked the women whether they were fasting or not .  
our laboratory uses the elecsys 25-oh d3 immunoassay ( leino et al . , 2008 ) for determination of 25-oh vitamin d3 levels .
this immunoassay is performed on a modular analytics e170 apparatus ( roche diagnostics , manheimm , germany ) .
the measuring range is 4 - 100  ng / ml ( 10 - 250 
nmol / l ) , the reference range for hypovitaminosis in our laboratory is <  30  ng / ml , corresponding the health based reference values .
vitamin d levels between 16 - 20  ng / ml are seen as mild deficiency , 6 - 16  ng / ml as moderate deficiency and values lower than 6  ng / ml as severe deficiency . for the statistical analysis
, we used spss statistics 17.0 ( spss inc . , chicago , illinois ) .
normality was tested with the kolmogorov - smirnov test , the means of vitamin d between all three groups were compared with anova - analysis .
the means of each group according to exposure were compared with an independent samples t - test . to compare the groups of women who used a prenatal vitamin and those who did not we also used the independent samples t - test .
linear regression was used to analyse wether vitamin d level is influenced by gestational age , maternal age , parity , gravidity , sun exposure , intake of supplements and/or date of blood sample .
for all tests significance was accepted at p  <  0.05 . the odd s ratio between covered and non - covered women with vitamin d levels lower than 30 
ng / ml was calculated , and 95% confidence intercal group were also compared using the chi squared test .
we determined 25-oh vitamin d3 in 171  women ( n  =  171 ) .
the mean age of this population was 29,1    4,6 ( standard deviation or sd ) years .
the median gestational age was 24  weeks ( range : 4 - 37 ) , most women were primiparae ( 72/171 , 42,1% ) .
the number of fasting women was too small ( 4/171 , 2,3% ) to draw any conclusions .
17% ( n  =  29 ) of the women was taking a multivitamin preparation .
they all used the same brand containing 10  microgram ( 400  iu ) of vitamin d. in the entire population the mean 25-oh vitamin d value was 28    12,4 ( sd ) ng / ml . there was no effect of age , gravidity , parity , intake of supplements nor gestational age on the vitamin d level .
there was however a statistically significant influence of date of blood sampling and sun exposure ( p  =  0,001 ) .
the mean vitamin d value of women taking supplements was 28,5    12,5 ( sd ) ng / ml , the group without supplements had a mean of 27,9    12,5 ( sd ) ng / ml . the difference in means between these two groups was not significantly different ( p  =  0,8 ) .
of all women 86% ( n  =  147 ) was not covered , 10,5% ( n  =  18 ) wore head covers but had other body parts exposed to the sun , 3,5% ( n  =  6 ) was completely covered , leaving only the face open for sun exposure .
there was a significant effect of degree of body covering on vitamin d level ( linear regression , p  <  0,001 ) .
the mean 25-oh vitamin d value in the non - covered group was 29,5    12,2 ( sd ) ng / ml . there was a significant difference in vitamin d level between the three groups ( anova , p  =  0,001 ) ( fig .  1 ) .
the mean of the partially veiled group , 17,2    7,2 ( sd ) ng / ml , was significantly lower than the mean of the non - veiled group ( t - test , p  =  0,001 ) .
the mean of the completely veiled group , being 22,5   12,9 ( sd ) ng / ml was not significantly higher than that of the partially veiled group and not significantly lower than the non - veiled group ( t - test , p  >  0,05 ) .
when we only compare covered versus non - covered groups , there are significantly more covered than non - covered women with a concentration of vitamin d lower than 30  ng / ml ( odds ratio 6,2 ; 95% ci : 1,8 - 21,7 ; p  <  0,05 ) .
the mean vitamin d value of our population , 28  ng / ml , was below the reference range used in our laboratory .
this suggests a widespread shortage of vitamin d in our population , 1,75% was suffering from severe deficiency , 9,9% had moderate deficiency and 18,1% had mild deficiency .
the values used are based on concentrations that avoid development of rickets and osteomalacia ( vieth et al . , 2007 ) . with new date on the role of vitamin d besides bone metabolism
, some authors are pleading for higher cut - off values to determine deficiency ( norman et al .
heaney ( 2005 ) states that 32  ng / ml should be considered as a minimum for normal physiology , bischoff - ferrari ( 2008 ) defines values of 36 - 40  ng / ml as optimal serum concentrations .
we found no effect of maternal age , gestational age , parity , gravidity and intake of supplements on the vitamin d level .
no consensus exists on the recommended intake and supplementation of 25-oh vitamin d during pregnancy .
, 2007 ; madelenat et al . , 2001 ; saadi et al . , 2007 ;
, 2009 ; yu et al . , 2009 ) and several authors agree that the current recommended intake of 200 - 600  iu ( or 5 - 15  g ) is too low , daily requirements may be closer to 1000 iu ( 25  g ) or higher ( bisschof - ferrari et al .
the most commonly prescribed multivitamin preparation in belgium , only contains 10  g ( 400  iu ) of vitamin d , a value that will not suffice to maintain or build sufficient levels .
this fact is confirmed in our pilot study : no significant difference in vitamin d levels between women taking supplements and those who did not .
there clearly was an effect of sun exposure and date of sampling , probably because august has more sun hours than november . in the population studied , the non - covered women had higher mean serum concentrations of vitamin d compared to partially covered women .
the higher mean values of the completely covered group were probably due to small group size and were not statistically significant compared with other groups .
however , we did not classify the participants according to their nationality nor their skin tone and as most women wearing head / body cover also have a darker skin , this is a fact that we should have taken into account
. furthermore , most of the covered women are immigrants who often live in poorer social circumstances .
hence , their lower vitamin d levels might not be only attributable to wearing head / body cover but also to poor dietary intake .
although most of the vitamin d production comes from skin conversion , the dietary intake of vitamin d is something we ll have to examine in further studies , as well as darkness of skin and nationality .
as this was a pilot study , we only measured 25-oh vitamin d. in the future , we will start including other relevant parameters such as medical history , serum levels of calcium and parathyroid hormone .
low vitamin d levels are frequently found in pregnancy but the optimal serum concentration remains unknown .
, we found that low vitamin d levels in the antwerp population are frequent and that there is an effect of the seasonal moment of the year and degree of sun exposure .
a large scale study is needed to come to clinical guidelines and recommendation for obstetricians .
 introduction : vitamin d deficiency in utero or early neonatal life may have a major impact on children s health . 
 little is known on vitamin d deficiency in pregnant women in belgium , non on the impact of wearing head and/or body cover.objectives : this was a preliminary exploration of the vitamin d status in pregnant women visiting the antenatal clinic in the antwerp university hospital.method : from august 1 2009 until november 30 2009 we systematically determined 25-hydroxy vitamin d ( 25-oh vitamin d ) in each blood sample taken from pregnant women visiting the antenatal clinic . 
 we also registered the degree of head / body cover and inquired for intake of vitamin supplements.results : our population consisted of 171  women , mostly primiparous , of which 86% were not covered . 
 the mean value of 25-oh vitamin d was 28  ng / ml . 
 non - covered women had a mean of 29,5    12,2 ( sd ) ng / ml , the partially covered group had a mean of 17,2    7,2 ( sd ) ng / ml and the completely covered group had a mean of 22,5    12,9 ( sd ) ng / ml . the difference in serum concentrations between the 3 groups was statistically significant ( anova , p  <  0,00001 ) . 
 there were significantly more covered than non - covered women with a vitamin d concentration lower than 30  ng / ml ( or6.2 ; 95% ci : 1,8 - 21,7 ; p  
 <  0,05).there was no effect of gestational age , maternal age , gravidity , parity and intake of supplements on vitamin d levels . 
 there was a siginificant seasonal effect from summer to fall , with vitamine d levels lowering from august to november ( linear regression , p  <  0,05).conclusion : low vitamin d levels seem to be frequent and covered woman are at a higher risk of deficiency . 