Why Pre-Pregnancy Screening Must Be Repeated Despite Previous Negative Results
Pre-pregnancy screening must be repeated in subsequent pregnancies because a previous negative result does not protect against new infections or changing risk factors between pregnancies, and the interval between pregnancies represents a new window of exposure risk.
Key Reasons for Repeat Screening
Risk of New Infection Between Pregnancies
The interval for re-screening should take into account changes in sexual partners, as women with previous negative screening tests may acquire new infections if their risk profile changes 1.
Even in women presumed to be at low risk (e.g., in mutually monogamous relationships with previous negative screening), rescreening at 6-12 months may be appropriate for previously infected women because of high rates of reinfection 1.
Each pregnancy represents a distinct time period with potentially different exposure risks, and infections like Chlamydia trachomatis—the most common sexually transmitted bacterial pathogen in the United States with 3 million new infections annually—can be acquired at any time 1.
Timing-Specific Pregnancy Risks
Screening early in pregnancy provides greater opportunities to improve pregnancy outcomes, including low birth weight and premature delivery, while screening in the third trimester may be more effective at preventing transmission of infection to the infant during birth 1.
For Chlamydia specifically, repeat screening during the third trimester is recommended for women aged <25 years or those at increased risk, with studies showing CT positivity rates of 3.3-3.5% on repeat screening in pregnant adolescent and young adult women during the third trimester 1.
Among women who were CT-negative at their first prenatal visit, 2.9% were CT-positive at third trimester rescreening, demonstrating that new infections occur during pregnancy itself 1.
Risk Factors Are Dynamic, Not Static
Age is the most important risk marker, and other patient characteristics associated with higher prevalence of infection include being unmarried, African-American race, having a prior history of sexually transmitted disease, having new or multiple sexual partners, and using barrier contraceptives inconsistently 1.
Individual risk depends on the number of risk markers and local prevalence of the disease, which can change between pregnancies based on life circumstances, new partnerships, or changes in community prevalence 1.
Prevalence of chlamydial infection varies widely among communities and patient populations, and a woman's risk profile may differ substantially from one pregnancy to the next 1.
Clinical Implications
Each Pregnancy Is an Independent Risk Assessment
A previous negative screening test does not confer immunity or ongoing protection—it only indicates the woman was not infected at that specific point in time 1.
The optimal interval for screening is uncertain, but for women with a previous negative screening test, the interval for re-screening should take into account changes in sexual partners 1.
Consequences of Missed Infections
Chlamydial infection can cause urethritis, cervicitis, pelvic inflammatory disease (PID) and result in ectopic pregnancy, infertility, and chronic pelvic pain in women 1.
Untreated infections during pregnancy can lead to transmission to the infant during birth, making third-trimester screening particularly important for preventing neonatal complications 1.
Common Pitfalls to Avoid
Do not assume that a negative result from a previous pregnancy provides ongoing protection—each pregnancy requires fresh screening based on current risk factors 1.
Do not rely solely on maternal risk factors for screening decisions—even women in apparently low-risk situations can acquire new infections between pregnancies 1.
Do not skip third-trimester rescreening in high-risk groups (women <25 years or those with identified risk factors), as studies demonstrate significant rates of new infection acquisition during pregnancy itself 1.