A study of hundreds of women, carried out at Imperial College London, found that subtle changes to the bacteria present in the vagina were strongly associated with the mother's waters breaking early and preterm birth-the baby being born before 37 weeks. According to the researchers, the findings show that a shift away from the usual healthy balance of vaginal bacteria was associated with waters breaking early, and could have an impact on the health of mother and baby, including increasing the risk of sepsis for newborns.
During pregnancy babies are protected inside the amniotic sac, with the surrounding membrane rupturing as part of the normal birthing process when the mother's 'waters break' as a precursor to labour. However, when this occurs before 37 weeks, termed premature rupture of membrane (PPROM), the baby is likely to be born prematurely. After the membranes rupture, the baby remains without the protective membrane and is at increased risk of infection - as the vaginal bacteria spread upwards to the placenta and uterus. In order to reduce this risk, the women whose waters have broken early are given intravenous antibiotics.
Researchers from the Institute of Reproductive and Developmental Biology (IRDB) at Imperial looked at the impact of premature rupturing of the membrane and antibiotic treatment on the vaginal microbiota, taking swabs from the vaginas of pregnant women at different points during their pregnancy and analysing them to reveal the types of bacteria present, their proportions and any changes.
Samples were collected from a prospective group of 250 pregnant women with and without risk factors for giving birth prematurely - such as having a history of preterm birth or miscarriage - of which 27 did in fact have a premature birth. They also collected samples from a second, smaller group of 87 women who presented to hospital with premature membrane rupture.
Previous research has shown that over the course of pregnancy the bacteria that colonise the vagina become less diverse and are dominated chiefly by Lactobacillus species, the same type of bacteria found elsewhere in the body including the gut and mouth. Analysis of the team's samples revealed that premature membrane rupture was associated with a shift in microbiota, with a drop in Lactobacillus and an increase in other types of bacteria, including potentially harmful bugs such as Staphylococcus and Streptococcus.
The team also analysed samples from the small group of women with premature rupture before and after the preventative antibiotic treatment - oral erythromycin, four times a day for 10 days. Swabs were taken before treatment and then at 48 hours, one week and two weeks. For those women whose microbial makeup was dominated by Lactobacillus before the treatment, the antibiotics resulted in a decline in Lactobacillus and a greater diversity of bugs. However, in those women with reduced Lactobacillus to begin with, the treatment was beneficial in some, reducing the amount of potentially harmful bacteria as well.
The study also revealed associations between specific vaginal bacteria and newborns who developed sepsis following delivery. While the mothers of healthy babies were dominated by Lactobacillus, samples from the mothers of newborns with sepsis revealed a greater diversity of bacteria, including the presence of Streptococcus and E. coli.
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