Dietary advice in preparation for, and during, pregnancy is aimed at reducing both the risks of birth defects and of having an infant of low birth weight that is at increased risk of poor health. Observational studies in this area have yielded conflicting results, mainly because so many aspects of the pregnant woman’s life vary with diet and nutrition. Dietary restriction in pregnancy causes decreased birth weight but it is not clear whether this is associated with an effect on morbidity and mortality. Nutritional protein supplements may lead to a modest increase in birth weight but no other benefits are recognised. Energy supplements appeared to be associated with enhanced fetal growth. Postnatal follow up has only been addressed in a few trials and in these there was no evidence of a lasting size advantage or improved cognitive development. During fetal development, the formation and closure of the neural tube occurs in two stages, primary and secondary neurulisation.