Cervicovaginal microbiome in twin vs singleton gestations

The vaginal microbiome diversity profile varies by race and ethnicity and changes considerably from the nonpregnant state to the pregnant state, specifically with a shift to Lactobacillus predominance in singleton gestations. There is a paucity of data that evaluate the cervicovaginal microbiome in women with twin gestations as a distinct population from those with singleton gestations.

We sought to characterize the cervicovaginal microbiome diversity profiles among twin gestations in the second trimester of pregnancy.

In this prospective cross-sectional cohort study, women with twin gestations were matched to singleton controls without a history of a short cervix or preterm birth by gestational age ±2 weeks and race. Cervicovaginal lavage samples were collected from 14 to 24 weeks of gestation during prenatal visits followed by a cervical length measurement. Cervicovaginal microbiota were analyzed with 16S RNA gene sequencing and classified into community state types based on Lactobacillus species predominance. Microbiome alpha and beta diversities were compared between twin and singleton gestations.

A total of 19 twin gestations and 19 singleton gestations underwent second-trimester cervicovaginal microbiome analysis. The groups were similar in gestational age at sample collection, maternal age, parity, body mass index, preterm birth history, and comorbidity. The cohort was predominantly of Black race (79%). Of twin gestations, 79% were dichorionic and diamniotic and 21% monochorionic and diamniotic. Of note, 3 twin gestations and 1 singleton gestation were complicated by a short cervix (P=.6). The vaginal microbiome of twin gestations had decreased alpha and beta diversities compared with singleton gestations. Twin gestations had lower taxon abundance and decreased variability in taxon abundance than singleton gestations. Overall, there was decreased diversity of community state type groups among twin gestations compared with singleton gestations. Community state types I and III were more prevalent among twin gestations, whereas community state types II and IV were similar among these 2 groups. Community state type IV, which is defined by a lack of Lactobacillus species and the presence of diverse strict anaerobes, was the predominant type among microbiota profiles of twin gestations (55%) and singleton gestations (64%). Community state type V was more prevalent in singleton gestations. When stratified by race, we found similar alpha diversity in Black and non-Black patients with twin gestations.

In our predominantly Black population of pregnant women, the second-trimester vaginal microbiome in twin gestations showed decreased alpha and beta diversities compared with singleton controls. Our findings increased the understanding of the content of microbial communities in the second trimester of pregnancy in twin gestations and suggested a potential mechanism for preterm birth in twin gestations.