Population-Based Study of Prediagnostic Antibodies to Chlamydia trachomatis in Relation to Adverse Pregnancy Outcome

Chlamydia trachomatis infection is one of the most common sexually transmitted reported bacterial infections worldwide. The well-known sequelae of chlamydial infection include pelvic inflammatory disease and tubal factor infertility, but the evidence linking C. trachomatis infection and adverse pregnancy outcome is inconsistent and has been largely based on case-control studies with limited study populations. We evaluated this link in a population-based longitudinal biobank health registry setting.

The association between C. trachomatis major outer membrane protein (MOMP) peptide-specific IgG antibodies and ectopic pregnancy, miscarriage, and preterm delivery was examined in a prospective case-control study nested in the Finnish Maternity Cohort. Ectopic pregnancy and miscarriage cases were identified through the Hospital Discharge Register 1998-2005; cases with preterm deliveries were identified through the Finnish Medical Birth register 1988-2005. Control samples were retrieved from the Finnish Maternity Cohort serum bank. A total of 800 cases of ectopic pregnancy, 800 cases of miscarriage, and 1350 cases of preterm birth were included. Equal number of pregnant women without the outcome diagnosis served as controls. The cases and controls were matched by sampling time, at the serum sampling and postal code district.

Antichlamydial IgG antibodies were associated with ectopic pregnancy. Positive antibody levels were found in 21.0% of cases and 14.6% of controls (P = 0.001; odds ratio, 1.56; 95% confidence interval, 1.20-2.03). Previous exposure to C. trachomatis, as indicated by serum antibodies, doubled the risk of ectopic pregnancy within age and was highest among women 35 years or older. Antichlamydial IgG antibody rates between the cases with miscarriage (16.3% in cases vs. 16.8% in controls) or preterm delivery (18.1% vs. 18.1%) and controls did not differ.

Our findings confirm the association between previous exposure to C. trachomatis and ectopic pregnancy. We found no association between C. trachomatis seropositivity and miscarriage or preterm birth.