The amount of stress experienced by both the mother and fetus during labor and delivery varies considerably and is likely to be different in primiparous and multiparous women. In this study we explored relations between the birth experience and lactation performance of 40 women. Stress hormones were measured in serum or plasma during pregnancy, parturition (cord and maternal blood), and lactation. Milk samples were obtained and breast-feeding frequency was recorded each day during the first 2 wk postpartum. Four outcomes were used as markers of lactogenesis: the time when the subject first felt fullness in the breasts, 24-h milk volume on day 5 postpartum, milk lactose concentration on day 5, and the day of appearance of casein in the milk as determined by gel electrophoresis. There were significant intercorrelations among the outcome variables, except for milk lactose. Compared with multiparous women, primiparous mothers experienced a delay in breast fullness and lower milk volume on day 5. In multiple regression analyses excluding subjects who had cesarean deliveries (n = 5), markers of both fetal and maternal stress during labor and delivery (cord glucose concentration and maternal exhaustion score) were associated with delayed breast fullness and casein appearance; delayed casein appearance was also associated independently with a longer duration of labor. Milk volume on day 5 was lower in women with higher exhaustion scores, and, in multiparous women, those who breast-fed less frequently on day 2. The milk lactose concentration was inversely related to pregnancy weight gain. These results indicate that primiparity, long labor, stress to the mother and fetus during labor and delivery, and elevated cord glucose concentrations are risk factors for delayed lactogenesis.