P-459 Sexually transmitted infections in women and fecundability – A prospective cohort study
Authors: Foldager A , Mikkelsen E M , Ulrichsen S P , Hatch E E , Wise L A , Sørensen H T , Laursen A S D 
Published: June 2023

Study question

Does a previous infection with Chlamydia trachomatis (CT) or genital herpes simplex virus (HSV) affect fecundability, and does recency of infection play a role?

Summary answer

Previous infection with CT or HSV in women was not appreciably associated with fecundability. However, a recent CT infection was associated with slightly lower fecundability.

What is known already

Worldwide, 1 million people contract sexually transmitted infections (STIs) every day. CT and genital HSV infections are among the most common STIs. Untreated CT in women can cause pelvic inflammatory disease (PID), which can lead to scarring and narrowing of the fallopian tubes and the lower uterus, thus complicating the ability to conceive. Also, an association between genital HSV in women and PID has been suggested. However, it is uncertain to what extent CT and HSV infections in women are associated with fecundability, defined as the per-cycle probability of conception, and whether recency of the infection plays a role.

Study design, size, duration

We conducted a prospective cohort study of female participants included in two Danish preconception cohorts: SnartGravid.dk (‘Soon Pregnant’, 2007-2011) and SnartForældre.dk (‘Soon Parents’, 2011-ongoing). At enrollment, participants had to be non-pregnant, aged 18-45 years, in a relationship with a male partner, not using contraception or fertility treatment, and trying to conceive. Participants completed a baseline questionnaire and bimonthly follow-up questionnaires until conception or up to 12 months after study entry.

Participants/materials, setting, methods

We analyzed data from 10475 women. At study entry, participants reported if they had ever been diagnosed (including year of first diagnosis) with CT or HSV. Fecundability ratios (FRs) were calculated using proportional probability regression models and 95% confidence intervals (CIs). The analyses were adjusted for age, income, educational attainment, other STIs, and smoking, reported at study entry. The reference groups were either women with no CT or no HSV diagnosis.

Main results and the role of chance

At study entry, 2603 (24.9%) of participants reported a history of infection with CT, and 766 (7.3%) with HSV. Using life table methods, 84.7% of participants conceived within 12 cycles of follow-up. Compared with the reference group, the adjusted FR for women ever diagnosed with CT was 0.98 (CI: 0.93-1.04) and 0.96 (CI: 0.88-1.06) for women ever diagnosed with HSV. Compared with the reference group, a recent CT infection was associated with slightly lower fecundability: adjusted FRs for women diagnosed 0-2 years, 2-5 years, and more than 5 years before study entry were 0.84 (CI: 0.71-0.99), 1.01 (CI: 0.90-1.12), and 1.00 (CI: 0.93-1.07), respectively. The association between recency of a HSV infection compared to the reference group was less evident: adjusted FRs for 0-2 years, 2-5 years, and more than 5 years since study entry were 0.93 (CI: 0.72-1.21), 0.97 (CI: 0.77-1.22), and 0.91 (0.75-1.09), respectively.

Limitations, reasons for caution

Misclassification of exposure is possible, as CT and HSV infections are often asymptomatic and hence undiagnosed. In addition, self-report may have resulted in misclassification of infection type and year. Further, we lacked information on severity or frequency of infections.

Wider implications of the findings

Women diagnosed with STIs often experience psychological distress concerning their future ability to conceive. Our finding of no overall association between previous diagnoses of CT or HSV may reassure women wanting to conceive. Still, testing for STIs remains important because untreated infections can damage the female reproductive system.

Trial registration number

Not applicable