['Our purpose was to compare the rate of adverse pregnancy outcome in pregnant mice with lower genital tract chlamydial infection who had a prior short chlamydial infection versus a prior long-term infection.', 'A total of 127 female mice were divided into short-term and long-term infection groups. We infected the lower genital tracts with Chlamydia trachomatis. After 7 days in the short-term infection group and 30 days in the long-term infection group, we treated the mice with tetracycline-impregnated chow. After documentation of cure, the mice were mated and transvaginally reinfected with Chlamydia trachomatis. Forty-one of the 127 (32%) mice became pregnant. We noted the number of mice with fetal death and the number of pups present. We cultured the lower uterine segment and the pups for Chlamydia.', 'Seven of 21 (33%) mice in the short-term infection group had fetal deaths compared with 1 of 20 (5%) in the long-term infection group (p < 0.05). In the short-term infection group 21 of 21 (100%) mice had positive transvaginal chlamydial cultures after reinoculation compared with only 7 of 20 (35%) in the long-term infection group (p < 0.000004). Seventeen of 21 (81 %) mice in the short-term infection group had positive chlamydial cultures from the lower uterine segment versus 1 of 20 (5%) in the long-term infection group (p < 0.000001). Sixty-five percent of pups in the short-term infection group and none (0%) of the pups in the long-term infection group were positive for Chlamydia (p < 0.00001).'] Does prolonged prior infection with Chlamydia prevent adverse pregnancy outcome in a murine model?