Uterine endometrium microbiota and pregnancy outcome in women with recurrent pregnancy loss

To evaluate whether uterine endometrium microbiota (UEM) is associated with pregnancy outcome in women with recurrent pregnancy loss (RPL). This prospective cohort study enrolled 67 women who had a history of two or more RPL. They underwent endometrial biopsy at midluteal phase for UEM analyses with 16 S ribosomal RNA sequence. Four women with inappropriate specimens were excluded. Therefore, 63 women were followed up for more than 14 months; 44 became pregnant, while 19 did not. Thirty of the 44 pregnancies ended in live births, including 24 full-term and six preterm deliveries. Three pregnancies were ongoing, and the remaining 11 ended in miscarriages, including eight miscarriages with normal chromosome karyotype and three miscarriages with abnormal karyotype. Clinical characteristics and UEM associated with risks for non-pregnancy, miscarriage with normal karyotype, and preterm delivery in subsequent pregnancies were evaluated. Multivariable logistic regression analyses revealed that the number of previous miscarriages (odds ratio 42.2, 95 % CI 1.19-1490, p = 0.040) and relative dominance rate of Ureaplasma species (odds ratio 24.2, 95 % CI 1.55-377, p = 0.023) in UEM were independent risk factors for subsequent miscarriage with normal karyotype; and relative dominance rate of Ureaplasma species in UEM was a risk factor for preterm delivery (odds ratio 109, 95 % CI 1.07-1110, p = 0.047). This study demonstrated for the first time that increases in Ureaplasma species in UEM of women with RPL were risks of miscarriage with normal chromosome karyotype and preterm delivery in subsequent pregnancies. UEM analysis for women with RPL before pregnancy may identify microbiota associated with adverse pregnancy outcomes.