OBJECTIVE: 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.

STUDY DESIGN: 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.

RESULTS: 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).

CONCLUSIONS: We conclude that in this murine model a prior 30-day genital tract infection with Chlamydia protects pregnant mice from subsequent reinfection and adverse pregnancy outcomes. (Am J Obstet Gynecol 1997;176:745-50.)