Background: Metformin is increasingly used in women of reproductive age and is known to cause vitamin-B12 malabsorption.

Aim: This audit aims to identify a relationship between maternal vitamin-B12 concentrations and metformin use in a population of pregnant women attending Endocrinology clinics in Western Sydney.

Methods: This audit reviewed data from pregnant patients attending two centres in Sydney between August 2007 to November 2011. Women with pregestational diabetes who had vitamin-B12 concentration tested during pregnancy were identified. Women with metformin use prior to and at the time of conception were compared to women without metformin use.

Results: Between 2007 and 2011, 83 pregnant women were identified to have vitamin-B12 levels tested. The mean age was 32.3±6.6 (metformin group) and 32.8±5.1 (no metformin group), 47 pregnant women had a history of metformin use and 36 women did not. The median vitamin-B12 level in pregnant women with metformin use was 178.0 pmol/L (130 – 249; 25th-75th percentile) and in pregnant women without metformin use was 278.5 pmol/L (177 – 353; 25th-75th percentile), p=0.011 by Mann-Whitney U Test. Ten women with a history of metformin use were vitamin-B12 deficient (normal: 125-780 pmol/L) compared to two woman amongst those who did not use metformin (p=0.040 by Pearson Chi-Square).

Conclusion: Significantly lower vitamin-B12 levels were identified in pregnant women with metformin use. The difference in actual vitamin-B12 levels between women with metformin use and women not taking metformin prior to gestation was statistically significant in this audit.