Potential risks and benefits of probiotics The World Health Organisation defines probiotics as live micro-organisms that confer a health benefit on the host when administered in adequate amounts. They can displace and kill pathogens, and modulate the immune response by interfering with the inflammatory cascade that can cause preterm labour. Administration of probiotics by mouth or intravaginally is safe and effective in reducing the incidence of or treating urogenital infections. There is no evidence of adverse consequences for mothers or their infants as a result of probiotic exposure during pregnancy. Acceptability of and compliance with daily ingestion of probiotic or placebo for a few weeks during mid-pregnancy was found to be high. The particular probiotic strains proposed for this study have been shown to be acceptable to and safe in pregnant women, and can colonise the vagina within 4 weeks of commencing oral intake.