Some inherited metabolic disorders (IMDs) can cause significant complications during pregnancy, affecting the mother and/or the fetus. Although it appears that only a minority of IMDs have these effects, experience is still being acquired. For some disorders, patients will not have reached child-bearing age. Pregnancies in this group of patients will increase as the management of IMDs in childhood and adolescence improves. Clinicians should be aware of potential complications and consider carefully how best to manage these conditions. Ideally, patients should be followed up in adult life by a specialized clinical team, which can implement a planned approach to conception and pregnancy, but often this is not possible. For disorders where the risk of complications is well established (e.g. phenyl-ketonuria), optimal treatment may lead to a good fetal and maternal outcome. It is important also to consider the possibility of an IMD being present in fetuses of pregnancies that are affected by non-immune hydrops, maternal HELLP syndrome (haemolysis, elevated liver enzymes and low platelets) or acute fatty liver of pregnancy.