BackgroundFetal chylothorax is associated with elevated perinatal mortality. Development of mediastinal shift with significant lung compression before 35 weeks' gestation needs treatment.CaseA 24-year-old gravida 2, para 0 presented at 26 weeks' gestation with a fetal pleural effusion with a mediastinal shift and abnormal Doppler velocimetry indices in several vessels. Thoracentesis was successful but 3 days later, the fetal effusion had reaccumulated. Because of fetal position, a pleuro-amniotic shunt was difficult technically, so maternal medical treatment was initiated with a low-fat, high medium-chain triglyceride diet. After initial mild decrease, the estimated volume of the fetal chylothorax remained stable until 36 weeks' gestation, at which time we delivered by cesarean an infant with good Apgar scores. After aspiration of the remaining thoracic fluid and administration of a similar diet, the infant did well, with normal growth and development.ConclusionMaternal dietary treatment might help delay the need for thoracentesis in cases of fetal chylothorax.