Aim To assess Vitamin D status in a multiethnic pregnant population and to explore the effect of skin colour as a risk factor.
Methods The study was conducted at a large District General Hospital with approximately 5000 births per year. Self assigned ethnicity and other demographic data including age, body mass index, parity gestation and date of sampling, was extracted from the maternity database. Skin colour was derived from this self-declared ethnicity. Specimens were obtained from existing serum serology samples collected from pregnant women at their booking appointments. A data list was obtained for the 4864 deliveries between April 2008 and March 2009. A random anonymised sample of 384 women was selected using Microsoft Excel of which 346 had sufficient serum for analysis. Samples were analysed for 25 hydroxyvitamin D by Liquid Chromatography, tandem mass spectrometry. Levels <25 nmol/l were defined as deficient.
Results 76 (22%) of the women were Black, 165 (48%) Asian, and 105 (30%) were Caucasian. There was no statistically significant difference in ethnicity between women selected and not selected in the sample. Black and Asian were classified as ‘dark’ and Caucasian as ‘light’ skinned. 91% of the samples were taken in the first or second trimester. 125 of 346 (36%) had Vitamin deficiency. 80% of dark skinned women and 29% of light skinned women had levels below 50 nmol/l. The median levels of 25 hydroxyvitamin D were significantly lower in the dark skinned group; median 25.70 nmol/l compared to the light skinned group; 70.5 nmol/l (p<0.0005; figure 1) There was no significant association with deficiency and gestation, obesity or parity in this sample.
Conclusion This is the first multi ethnic population versus clinic sample in England which describes widespread vitamin D deficiency in pregnancy. Over a third of our population were deficient (<25 nmol/l), dark skinned mothers having more than double the risk of light skinned mothers despite a national policy of vitamin supplementation in the antenatal period. The questions remain of how well is this policy is being implemented and what is the optimum the dosage and method of supplementation. A recent BPSU study has been approved to estimate the incidence of hypocalcaemic neonatal convulsions because of increased paediatric concerns in the UK.