The increase in allergic disease among children in the developed world is widely believed to be due to reductions in exposure to infective agents (the hygiene hypothesis). One way to counteract this is by exposing pregnant women to beneficial bacteria, such as probiotics. Using a randomised controlled double-blinded trial, we aim to investigate the effect of L rhamnosus HN001 taken daily (1010 CFU) by pregnant women from the first trimester of pregnancy and during breast feeding until 6 months post-partum on the development of eczema and atopic sensitisation in their infants at age 12 months. The effects of this probiotic on maternal health in pregnancy, including gestational diabetes mellitus, group B streptococcal vaginal infection and bacterial vaginosis will also be investigated as secondary outcomes. Probiotics are a cheap and safe intervention that may prevent cases of eczema and allergy in infancy and improve pregnancy outcomes for women.