We report on eleven pregnancies in 5 mothers. 6 of the babies had long-chain 3-hydroxyacyl coenzyme A dehydrogenase (LCHAD) deficiency, and each of the pregnancies was complicated by features such as fatty liver and HELLP (haemolysis, elevated liver enzymes, low platelets) syndrome. By contrast, 3 of the mothers also gave birth to unaffected babies, and these pregnancies were largely uncomplicated. We conclude that there may be adverse effects on maternal liver function from a fetus with LCHAD deficiency. Heterozygosity in the mother cannot alone account for the adverse effects because of the segregation of these effects with fetal LCHAD status.