['In Africa, lactational amenorrhea is the major reason for birth spacing.', 'We studied whether the early introduction of complementary food to infants is associated with an increased risk of menstruation resumption in rural African women.', 'Senegalese women (n = 855) were included at 2-3 mo postpartum and followed up at 4-5 and 6-7 mo in dispensaries. A subsample of 502 women were followed up at 9-10 mo and twice yearly at home thereafter. Risk factors for menstruation resumption were assessed with logistic regression, with control for maternal parity, occupation, education, postpartum body mass index, child sex and weight-for-age, and season.', 'The risk of menstruation resumption was 4.2% (95% CI: 2.8%, 5.6%) at 6-7 mo and 6.5% (4.0%, 8.9%) at 9-10 mo. Compared with the introduction of complementary food after 6-7 mo, introduction at 2-3, 4-5, or 6-7 mo was associated with a greater odds of menstruation resumption at 6-7 mo [odds ratios (ORs): 5.08 (1.01, 25.5), 6.00 (1.29, 27.4), and 4.45 (0.96, 20.6; NS), respectively]. Introduction of food at 4-5 or 6-7 mo compared with that after 6-7 mo was associated with significantly greater odds of menstruation resumption at 6-7 mo (5.13; 1.16, 22.6) but not at 9-10 mo (3.07; 0.65, 14.4; NS) or year 2.'] Is lactational amenorrhea associated with child age at the time of introduction of complementary food : a prospective cohort study in rural Senegal , West Africa?