How common are chlamydia-related bacteria in early pregnancy and are they associated with miscarriage or preterm birth? Community-based prospective cohort study

Abstract

BackgroundSerological case-control studies suggest that certain chlamydia-related bacteria (Chlamydiales) that cause cows to miscarry might do the same in human beings. Included in the order Chlamydiales are Waddlia chondrophila, Chlamydophila abortus, and Chlamydia trachomatis. We aimed to investigate the prevalence of Chlamydiales in pregnant women, and possible associations with miscarriage or preterm birth. MethodsWe tested stored urine samples from a carefully characterised cohort of 847 pregnant women recruited at mean 49·3 (SD 10·1) days’ gestation from 37 general practices in London, UK. Previous repeat testing of samples positive for Mycoplasma genitalium confirmed bacterial DNA integrity after storage. W chondrophila and pan-Chlamydiales specific real-time PCRs targeting the 16s rRNA gene were used to test samples. Samples positive on either of the two PCRs were subjected to DNA sequencing and Chlamydia trachomatis PCR. Outcomes were compared between infected and uninfected women with Fisher's exact test. Ethics review was conducted by Wandsworth, Croydon, and Riverside Research Ethics Committees. FindingsThe overall prevalence of Chlamydiales was 4·3% (36/847, 95% CI 3·0–5·8). Prevalence of W chondrophila was 0·6% (5/847, 0·2–1·4), Chlamydia trachomatis 1·7% (14/847, 0·9–2·8), and other Chlamydiales species 2·0% (17/847, 1·2–3·2). Infection with Chlamydia trachomatis (but not with other Chlamydiales or W chondrophila) was more common in women younger than 25 years, of black ethnicity, or with bacterial vaginosis. Follow-up was 99·9% (846/847) at 16 weeks’ gestation and 89·6% (759/847) at term. No infection was significantly associated with miscarriage (prevalence 10%, 84/827) or spontaneous preterm birth before 37 weeks’ (4%, 23/628) but numbers were small. One of three (33%) followed-up women infected with W chondrophila had a preterm birth compared with 22 (4%) of 625 uninfected women (p=0·11). Sequencing of 25 samples that were positive on W chondrophila or pan-Chlamydiales PCR revealed seven samples (28%) positive for Chlamydiales bacterium sequences that have been associated with respiratory tract infections in children. Interpretation4% of newly pregnant women tested positive for Chlamydiales, including species known to be pathogenic in mothers and neonates. Higher rates might have been found in vaginal samples and the study lacked power to test associations. Although W chondrophila might be associated with preterm birth, the prevalence was very low in this urban, community-based sample, suggesting that screening is unlikely to be cost-effective in such a population. FundingMedical Research Council.