The vaginal microbiota varies by self-identified ethnicity and HIV status throughout pregnancy and relates to preterm birth risk in a United Kingdom observational cohort

Black pregnant women living with HIV showed the highest rates of preterm birth, and transitions in vaginal microbiota during pregnancy were linked to increased risk, especially between certain community state types.

Summary and findings

This study measured vaginal microbiota composition and preterm birth (PTB) risk among pregnant women living with HIV (PWLWH) and without HIV (PWWH) in the UK. A total of 103 women participated, with 12 experiencing PTB, primarily among Black PWLWH. The findings indicated that CST transitions were associated with PTB risk, particularly among Black PWLWH.

Abstract

<title>Abstract</title> <p> Background Low-diversity, <italic>Lactobacillus</italic> -dominated vaginal microbiota are associated with immune protection in pregnancy, whereas community state type (CST) IV and transitional CST III are linked to inflammation and preterm birth (PTB). Pregnant women living with HIV (PWLWH) in the UK have higher preterm birth rates than pregnant women without HIV (PWWH). We previously identified an association between PTB and CSTs III and IV in PWLWH from the UK HIV Preterm Birth Network study. However, participants in that cohort predominantly self-identified as having a Black ethnic background, and it remains unclear whether these associations differ according to HIV status and social factors. This larger analysis compares vaginal microbiota composition, inflammation, and PTB outcomes across self-identified Black and White PWLWH and PWWH. Results 103 women (55 Black PWLWH, 14 Black PWWH, 15 White PWLWH, and 19 White PWWH) provided second trimester vaginal samples. Twelve women experienced PTB, 10 of whom were Black PWLWH (18.2% PTB rate). Black pregnant women had higher Chao1 alpha diversity than White PWWH (p = 0.002). CSTs III and IV were more prevalent in Black women and White PWLWH, while CST I was less frequent. Among Black women, HIV was not associated with Chao1 diversity or inflammation, whereas among White women, HIV was linked to heightened Chao1 (p = 0.007) and increased cervicovaginal cytokines. In Black PWLWH who experienced PTB, most were assigned to CST III or IV in the second trimester. Nearly half of Black PWLWH (49%) underwent a CST transition during pregnancy and were more likely to transition compared to other subgroups (aOR: 2.53, 95% CI 1.02–6.52; p = 0.048). CST change trended toward increased PTB risk in Black PWLWH (aOR: 3.50, 95% CI 0.82–18.46; p = 0.10), with transition between CSTs III and IV associated with the highest risk of PTB (aOR: 7.75, 95% CI 1.57–42.75; p = 0.01). Conclusions Black PWLWH had the highest PTB rates, and CST instability during pregnancy was associated with PTB risk in this group, particularly transitions between CSTs III and IV. The high prevalence of CSTs III and IV among Black women regardless of HIV, and within White PWLWH, may reflect broader socioeconomic determinants of reproductive health. </p>

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