The impact of maternal oral microbiota on the risk of small vulnerable newborns: a nested case-control study

Small vulnerable newborns (SVNs) account for most neonatal deaths worldwide. Though maternal periodontal disease has been shown associated with an increased risk of preterm birth (PTB) and low birth weight (LBW), little evidence shows the potential mechanism. Our study aimed to explore the association between maternal oral microbiota and SVNs before and during pregnancy.

A nested 1:4 case-control study was undertaken. Women delivering SVNs, including spontaneous PTB, LBW, and small-for-gestational-age (SGA) newborns, were selected as cases, while women delivering normal newborns were randomly selected as controls. 480 unstimulated saliva samples were collected from 240 women (48 cases and 192 controls) in preconception and late pregnancy. 16 S rRNA gene sequencing was used for analysis.

Women with SVNs showed lower richness index (p = 0.032) in oral microbiota during preconception, lower shannon (p = 0.028) and simpson (p = 0.023) index in late pregnancy compared to the control group. Granulicatella and Streptococcus were significantly enriched in saliva both before and during pregnancy in women delivering SVNs. The two evaluated genera were positively correlated with enriched metabolic pathways like lactose and galactose degradation. These genera and their species were also enriched among women in the PTB and SGA sub-groups.

Women with SVNs exhibited significantly lower diversity in oral microbiota, with two enriched genera Granulicatella and Streptococcus in both before and during pregnancy.