Preventing Preterm Birth With Probiotics - Pilot Randomised Trial

Preterm birth (PTB) is defined as the birth of a baby before the completion of 37 weeks gestation in the womb. It is the major cause of infant mortality particularly during the first month of life. Approximately 75 per cent of babies who die during the first 28 days of life are born before 37 weeks gestation. Survivors of PTB are at increased risk of long-term disabilities such as cerebral palsy, sight and hearing impairment, learning and behavioural problems, epilepsy, and hospital readmissions. Even late preterm births, defined as PTB at 34--36 weeks gestation, which account for 70% of all preterm births in England and Wales, are at increased risk of death and disability compared with babies born at term. Although the prevalence of adverse long--term outcome is highest among children born at the earliest gestational ages, the much higher number of births at 34--36 weeks of gestation compared with earlier gestations means that this group of children makes a major contribution to the number of children adversely affected. PTB and its consequences can have negative emotional and psychosocial impacts on parents and families.

In addition to its impact on individuals and families, the financial consequences for the public sector of caring for children born preterm are significant. The cost of care up to the age of 18 for children born preterm has been estimated to exceed £3 billion per year in England and Wales at 2006 prices. It has been estimated that a hypothetical intervention that delayed PTB by 1 week across all gestational age categories would reduce the public sector cost of PTB by £1 billion annually.

About one third of PTBs occur because early delivery is indicated due to complications in the mother or the unborn baby (fetus); the remaining two thirds occur spontaneously. The rate of PTB has increased by 19% from 1990 to 2010 in developed countries. At the same time, there has been a marked improvement in the survival rates of PTBs but a similar reduction in adverse outcomes has not been seen. Thus, the absolute numbers of individuals adversely affected is increasing.

Infection within the womb (intrauterine infection) is strongly associated with spontaneous PTB. The commonest pathway for intrauterine infection is the ascent of unhealthy bacteria from the vagina and cervix into the womb. Bacterial vaginosis (BV), in which the normally dominant healthy bacteria in the vagina (lactobacilli) are replaced with unhealthy bacteria, is strongly associated with PTB. Lactobacilli, principally the strains that produce higher levels of the chemical hydrogen peroxide, appear to protect against BV and reduce the risk of PTB.

Despite substantial evidence linking BV with PTB, the results of trials of antibiotic treatment of BV in pregnancy have not produced clear evidence of benefit. The reason for this might be that it is not the eradication of unhealthy bacteria that is required but rather the replacement of unhealthy bacteria with the normally dominant lactobacilli. One way of achieving this could be by administering lactobacilli-containing capsules (probiotics) to pregnant women. Oral probiotics taken during pregnancy may directly alter the vaginal bacteria and in so doing protect the cervical opening from ascending infection.