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Abstract and Introduction
Abstract
Purpose of review The aim is to describe and quantify the association between genitourinary tract infections and preterm birth.
Recent findings Recent studies confirm the importance of identifying and treating both asymptomatic and symptomatic bacteriuria in pregnancy, which is reflected in current antenatal screening guidelines. These guidelines do not recommend routine screening for other asymptomatic lower genital infections (bacterial vaginosis, trichomonas and gonorrhoea) reflecting inconsistent study results, which may reflect differences in study design, size, diagnostics and the timing of screening in pregnancy. Screening for group B Streptococcus (GBS) late in pregnancy is recognized to reduce neonatal disease, but there is a striking lack of robust studies, specifically randomized controlled trials (RCTs), considering the effect of GBS screening earlier in pregnancy on adverse pregnancy outcomes.
Summary The potential for screening and treatment of genitourinary tract infections in pregnancy to reduce preterm birth rates has been demonstrated in some RCTs. Current guidelines do not reflect these data because of inconsistencies across the body of evidence. There is a need for robust RCTs to confirm or refute earlier data, to inform the optimal timing for screening in pregnancy and to better quantify the contribution of individual infections to the burden of preterm birth.
Introduction
Preterm birth remains a leading direct cause of mortality in children aged less than 5 years in both developed and developing country settings. The burden of child mortality attributable to preterm birth is reflected by the frequency of this pregnancy outcome: there were an estimated 14.9 million preterm births in 2010, accounting for 5% of births in some European countries and up to 18% of births in some African countries. The risk of death in preterm infants is further increased through greater susceptibility to conditions including neonatal infections. In the past decade, risk factors and mechanisms leading to prematurity have been identified including family history, maternal age, BMI, hypertensive disease of pregnancy and infection. The existence of different pathways contributing to its pathogenesis, as well as a poor understanding of their relative contributions, may explain why it remains so difficult to predict and therefore prevent preterm birth.
There are multiple recognized aetiologies underlying spontaneous preterm birth, and ascending genital tract infections may contribute to up to 50% of premature deliveries, particularly those occurring before 30 weeks of gestation, which are even more likely to be infection-related. The role of intrauterine infection in preterm birth has been demonstrated through studies reporting the association of chorioamnionitis and preterm birth with the subsequent recovery of bacteria from placentas or amniotic membranes of preterm births. The mechanism of action is thought to relate to the recruitment of leukocytes when infection reaches the endometrium triggering cytokine, and then prostaglandin, production that can lead to uterine contractions, cervical dilatation, membrane exposure and greater entry of pathogens in the uterine cavity. Cytokines also stimulate production of matrix metalloproteinases by the chorion and amnion, which have been implicated in. both cervical ripening and degradation of the fetal membranes.
Lower genital tract bacteria may also act locally, producing enzymes that may weaken protective cervical mucus production and promote bacterial invasion of the upper genital tract. This local action suggests a role for lower genital tract organisms with and without ascending infection, but their overall contribution to the burden of preterm births is poorly understood. Because preterm births represent a disproportionate percentage of neonatal morbidity and mortality, infection-associated preterm birth represents an attractive area for intervention and it is therefore important to quantify potential associations with different genitourinary pathogens. This article reviews the most recent evidence on the association of different genitourinary pathogens with preterm birth and discusses areas for future research.
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