Nutritional and antimicrobial interventions to prevent preterm birth: an overview of randomized controlled trials

The study was conducted to assess the effectiveness of interventions for the prevention or treatment of nutritional and infectious disorders during pregnancy on preterm birth rates. Cochrane systematic reviews or any other more up-to-date systematic review of antimicrobial and nutritional interventions were sought. Electronic searches of the Cochrane Controlled Trials Register were carried out to identify any trials published since the most recent update of the systematic review. Also, authors of Cochrane systematic reviews, which have not been updated recently, were contacted regarding new information. Systematic reviews of nutritional and antimicrobial interventions during pregnancy, reporting preterm delivery rates (delivery before 37 weeks) and "prematurity" (including low birth weight) either as primary or secondary outcomes, were included. General interventions without a specific nutritional supplementation or antimicrobial component were not considered for inclusion. Interventions to stop labor or prolong pregnancy after a diagnosis of preterm labor were excluded. For each systematic review, data on preterm delivery rate by intervention group was obtained. The total number of trials in the review, number of trials reporting preterm birth as an outcome, number of participants and events have been systematically extracted. Eighteen systematic reviews (10 nutritional and 8 antimicrobial) were considered. Our results indicated that, overall, the treatment of asymptomatic bacteriuria reduces the incidence of preterm birth or low birth weight (< 2500 gm) (typical relative risk (RR): 0.67; 95 percent confidence interval (CI): 0.52-0.85). The protective effect of treating asymptomatic bacteriuria for preterm delivery persisted when only the three trials reporting preterm delivery (< 37 weeks) were included in the meta-analysis (typical RR: 0.53, 95 percent CI: 0.33-0.86). Routine iron supplementation prevents maternal anemia and one trial comparing routine versus selective iron supplementation showed a statistically nonsignificant reduction in preterm birth. Zinc, magnesium, and fish oil supplementations show promising results in reducing preterm birth, but the evidence is not strong. Calcium supplementation remains controversial, although there was a statistically significant reduction in preterm delivery in the subgroup of women at high risk of developing hypertension during pregnancy. Two trials with use of metronidazole (alone or with erythromycin) showed a reduction in preterm delivery in women who were at a high risk of preterm delivery and had bacterial vaginosis at screening. We have concluded that asymptomatic bacteriuria should be screened and treated in all settings that offer antenatal care. Single dose treatment seems to be as effective as longer (4-7 days) treatment, although this needs to be confirmed by a large, methodologically rigorous trial. There are a number of promising interventions such as calcium supplementation in women with low calcium intake, iron, zinc, magnesium, and fish oil supplementation, and treatment of bacterial vaginosis in women at high risk of preterm delivery that need additional research to determine a possible role for prevention of preterm delivery.