In this presentation, Ashorn describes data on antibiotic use during pregnancy. As maternal infections are associated with intrauterine growth restriction and preterm births, theoretically presumptive or targeted antibiotic use in pregnant women may promote foetal growth and prevent preterm births. Data from the Lungwena Antenatal Intervention Study (LAIS), which investigated whether antimalarial treatment of pregnant women was associated with a reduction of preterm births, was presented. The study showed that intermittent preventive treatment of malaria in pregnant mothers with monthly sulfadoxine-pyrimethamine plus two doses of azithromycin reduced the incidence of preterm delivery and LBW(low birth weight) babies. The predictors of antibiotic efficacy in preventing SGA(small for gestational age) and preterm births were also discussed. Presumptive antimicrobial treatment may improve birth outcomes in some, but not all, contexts. General preventive treatment of maternal infections was more effective than those targeting only infections of the reproductive tract.