We investigated the cost-effectiveness of strategies for screening pregnant women for Chlamydia trachomatis. Screening was not cost-effective unless certain conditions were met. Direct antigen testing of all pregnant women would be cost-effective if the test cost less than $6.30 or the prevalence of infection exceeded 6%. However, the positive predictive value of the test was only 51%. Culturing was not cost-effective until the prevalence of infection exceeded 14.8%. If a direct antigen test cost less than $3.90 or prevalence exceeded 8.7%, direct antigen testing of all women and using culture to confirm positive direct antigen tests would be cost-effective. If a direct antigen test cost $8.00 and culture cost $25.00, the excess cost of performing a direct antigen test in all women and confirming positive results with culture would be $2.09 per pregnant woman. Screening all pregnant women for chlamydia is not cost-effective, but the excess cost is modest when direct antigen tests are used.