Postnatal transfer of high-risk infants to a neonatal intensive care unit has been an accepted medical practice for more than two decades. More recently, antepartum maternal referral for the smallest infants has been recommended to reduce infant mortality, morbidity, and long-term handicaps. The limited data available to compare in utero and postnatal transfer suggest that maternal risk factors may also influence antenatal referral. We evaluated antepartum maternal and postnatal infant referrals from five metropolitan Denver hospitals with level I facilities. Mothers who were referred to the tertiary perinatal center before delivery were more likely to have one or more high-risk conditions. The presence of a maternal risk factor (preeclampsia, antepartum bleeding, prolonged rupture of the membranes, or chorioamnionitis) was significantly more common in the maternal transfer group (p less than 0.002). Neonatal weight was higher for the maternal referrals compared with neonatal referrals. Neonatal survival was independently improved by transport of mother or infant, increasing birth weight, and higher Apgar scores. We suggest that maternal risk factors were an important determinant in the choice of antenatal referral to our perinatal center for both the community and regional hospitals during this study period. Studies that compare outcome of infants after maternal and infant transfer must control for potentially inherent differences between the antenatally and postnatally transferred infants.