Hyperemesis gravidarum is a complication of pregnancy that can lead to severe maternal nutritional deprivation. Total parenteral nutrition has been used in pregnancy complicated by hyperemesis gravidarum. However, little has been done to study the nutritional aspects of hyperemesis or the maternal effects of total parenteral nutrition when given during the first trimester of pregnancy. The purpose of this study was to examine the nutritional state of pregnancy complicated by hyperemesis gravidarum and the effects of total parenteral nutrition on maternal nutrition and fetal outcome when given during the first trimester of pregnancy. Using a standard method of indirect calorimetry, the basal metabolic expenditure and adjusted metabolic expenditure were determined, and appropriate calories were calculated for each patient. The patients were then started on total parenteral nutrition. Follow-up indirect calorimetry studies showed improved nutritional status, with return of anabolic parameters. The results of this study support the conclusion that total parenteral nutrition given during the first trimester is a safe and effective method of nutritional support.