['To determine: 1. whether abnormal umbilical artery Doppler studies were independently associated with newborn morbidity; and 2. whether small for gestational age babies with normal umbilical artery Doppler studies had small mothers and a low rate of newborn malnutrition and morbidity.', 'Prospective observational study.', "National Women's Hospital, a tertiary referral centre, Auckland, New Zealand.", 'One hundred eighty-six women and their small for gestational age babies (birthweight < 10th%) who had been participants in one of two randomised controlled trials of small for gestational age pregnancies between 1993 and 1997.', 'Newborn morbidity and morphometry were compared between small for gestational age babies with normal and abnormal umbilical artery Doppler studies (resistance index > 95th%). Maternal demographic characteristics and morbidity were also compared.', 'Compared with small for gestational age babies with normal umbilical artery Doppler studies (n = 109), small for gestational age babies with abnormal umbilical artery Doppler studies (n = 77) were diagnosed earlier in pregnancy as being small for gestational age (30.3 vs 32.9 weeks, P < 0.001), were smaller in all body proportions at birth (median Z score birthweight -1.82 vs -1.70, P = 0.004, Z score length -1.86 vs -1.36, P < 0.0001, Z score head circumference -1.31 vs -0.89, P < 0.0001) and were more likely to experience newborn morbidity. When birthweight and gestation were entered into a logistic regression model, an abnormal umbilical artery Doppler study was not an independent predictor of prolonged newborn nursery admission or hypoglycaemia. Of small for gestational age babies with normal umbilical artery Doppler studies, 53 (49%) had low ponderal indices, 26/98 (26%) were hypoglycaemic and 38 (35%) required admission to the newborn nursery. There was no difference in maternal height, weight and ethnicity between the abnormal and normal umbilical artery Doppler groups.'] Do umbilical artery Doppler studies in small for gestational age babies reflect disease severity?