To assess the significance of nuchal cords, 110 affected woman-infant pairs at term gestation were compared with 110 control pairs. Newborns with a nuchal cord had an increased prevalence of umbilical artery acidemia (22 of I10 versus 13 of 110; P <.05) and more variable fetal heart rate (FHR) decelerations in the first stage of labor (mild = 41 versus 20; P <.0001; moderate-severe = 21 versus 5; P <.0001) and the second stage of labor (moderate-severe = 46 versus 21; P <.0001). In newborns with a nuchal cord, the umbilical artery acidemia was usually mixed (68%) or respiratory (23%) in origin, and pure metabolic acidemia was infrequent (9%). We conclude that nuchal cords are associ- ated with an increased prevalence of variable FHR deceler- ations in the first and second stages of labor and with an increased incidence of umbilical artery acidemia. © 1987 by The American College of Obstetricians and Gynecologists.