Ultrasound examination at 9 weeks of gestation in a 34-year-old primigravida showed a twin pregnancy, with discrepancy in the sizes of the two gestational sacs, whereas the crownrump lengths and fetal heart rates were virtually identical – the result being an abnormal sac size/crownrump length ratio (early oligohydramnios). By 14 weeks discordant heart rates and umbilical artery flow velocities were detected, the discordance between the twins increasing as pregnancy progressed. Biparietal diameters, femoral lengths, and abdominal circumferences were also progressively discordant, and at 28 weeks the smaller twin had no heart beat. At 30 weeks the patient was delivered of a live 1,350-gram infant and a 400-gram dead fetus. This case suggests, in contradistinction to several previous reports, that fetal discordance in twin pregnancies (and perhaps intrauterine growth retardation in general) may be present as early as the first trimeste