GSTM1 and folate deficiency: Women missing a Hb result in the first 20 weeks of pregnancy were similar to those in the study population, but were less likely to have been born in Southern Asia, and more likely to have been born in Oceania, had 2 or more previous pregnancies, had a previous history of B12/folate deficiency, and have smoked during pregnancy (standardised difference >0.1).