O-262 The vaginal and faecal microbiome in women with recurrent pregnancy loss (RPL) before pregnancy according to the reproductive outcome after referral

Abstract Study question Is the vaginal or faecal microbiome different between primary RPL (pRPL) and secondary RPL (sRPL) patients, and is it related to reproductive outcome after referral? Summary answer Before pregnancy, the vaginal microbiome differed between pRPL and sRPL, and the faecal microbiome was altered in those who did not achieve pregnancy after follow-up. What is known already RPL is a heterogeneous condition leaving 50% of the couples without any known risk factors after the initial diagnostic workup. The microbiome of the reproductive tract seems to be an essential factor in women’s health, including pregnancy loss. Only a few studies have investigated the vaginal microbiome in women with RPL and found dysbiosis with a decrease in Lactobacillus crispatus. To our knowledge, the faecal microbiome in women with RPL has never been investigated. Study design, size, duration A prospective cohort study including 106 women referred with unexplained RPL between 04/2018 and 12/2019. Patients were routinely screened for established risk factors as recommended in the ESHRE RPL guideline. Exclusion criteria were >40 years, >1 shared child, the use of antibiotics, antimycotics and antiviral medication within the past two weeks, known chromosomal aberrations and major uterine malformations. Follow-up ranged between 12-31 months. Participants/materials, setting, methods The women were referred with a minimum of three unexplained consecutive pregnancy losses (64 pRPL and 42 sRPL) to the tertiary Recurrent Pregnancy Loss Unit at Copenhagen University Hospital (Rigshospitalet and Hvidovre Hospital), Denmark. Vaginal and faecal samples were collected before pregnancy and shot-gun sequenced on a DNBSEQ-G400 sequencer (MGI) using the high-throughput sequencing set (PE150 1000016952; MGI). Main results and the role of chance The beta diversity in the vaginal samples was significantly different (p = 0.001) between pRPL and sRPL, with Lactobacillus crispatus dominating more women with pRPL compared to sRPL who were dominated by Lactobacillus iners. Overall, twenty-nine patients (27.3% of the cohort) had vaginal dysbiosis defined as < 60% Lactobacillus spp. with no significant difference between pRPL and sRPL (vaginal dysbiosis in 21.8% vs. 35.7%, p = 0.118). During follow-up, 93 (87.7%) patients achieved pregnancy of which 50 (53.8%) resulted in a live birth and 43 (46.2%) in another pregnancy loss. There were no differences in age, BMI, alpha or beta diversity in the vaginal samples between the live birth group and pregnancy loss group. In the live birth group, 11 patients (22.0%) had vaginal dysbiosis compared with 32.1% of the rest of the cohort, p = 0.242. Ninety-three of 106 women collected a faecal sample at home after the first consultation and there was a significant difference in both alpha diversity (p = 0.014), beta diversity (p = 0.05) and richness (p = 0.001) between women who achieved pregnancy compared with those who did not conceive after follow-up. Limitations, reasons for caution Patients with recurrent pregnancy loss constitute a heterogenic population, which underlines the importance of subgroup comparisons such as pRPL and sRPL. Wider implications of the findings These findings underline the role of an altered vaginal and faecal microbiome as a potential risk factor for RPL. In-depth knowledge about the altered microbiome compositions in these patients can contribute to the generation of future treatment strategies and potentially improve patient care. Trial registration number not applicable