Associations between maternal salivary testosterone at 36 weeks’ gestation with birth weight and infant weight gain through 6 months of age were examined in a group of 49 healthy, pregnant women and their offspring. The diurnal decline of maternal testosterone was conserved in late pregnancy, and levels showed significant day-to-day stability. Elevated maternal morning testosterone level was associated with lower birth weight Z-scores adjusted for gestational age and sex, and greater infant weight gain between birth and 6 months. Although maternal testosterone levels did not differ by fetal sex, relations were sex-specific such that maternal testosterone had a significant impact on weight for male infants; among female infants associations were nonsignificant. Results highlight the opposing influence of maternal androgens during pregnancy on decreased growth in utero and accelerated postnatal weight gain.