54 Pregnant women and 216 without were detected for anti-Chlamydial antibodies, using indirect hemagglutination test on a 1:4 matched Case-control study to look for risk factors of Chlamydia trachomatis infection. A total number of 26 independent variables were selected for analysis, in which 8 factors were confirmed as associated factors by single variable analysis. Of the above 8 factors, 4 were significantly correlated to the infection under the multifactorial conditional logistic regression model, which were: extramarital sex life, history of urogenital tract infection, age of sexual intercourse debut and the use of intrauterus contraception.