A 26 year old woman with hepatic glycogen synthetase deficiency booked for antenatal care at 18 weeks of gestation in her first pregnancy. The condition had been diagnosed at the age of seven years (Aynsley‐Green et al. 1977) when she presented with nocturnal hypoglycaemic seizures. She was shown to have a pathognomonic metabolic profile characterised by fasting hypoglycaemia and hyperketonaemia with postprandial hyperglycaemia and hyperlactataemia. Glycogen synthetase activity was normal in muscle tissue but deficient in the liver. Regular high protein, small volume meals were recommended, including a snack at 2 am to avoid nocturnal hypoglycaemia. She had no further nocturnal seizures and the nocturnal snack was discontinued at the age of 15 years.

When seen in pregnancy, she was in good health. There were no symptoms of hypoglycaemia, especially before breakfast or during intercurrent illness. She measured 145 cm in height and 52.6 kg in weight. Blood pressure was 120/70 mmHg, the liver was not palpable and the fundal height was equivalent to 18 weeks of gestation. Fasting urinalysis was negative for ketones. An ultrasound scan showed that the fetal size was consistent with dates and no fetal abnormality was detected. Symphysio‐fundal height and serial ultrasound examinations revealed that fetal growth was normal. She remained well in pregnancy without alteration in diet.