Pregnancy is a physiologically and immunologically challenging health state. Immunological and physiological changes throughout the course of pregnancy make pregnant women usually susceptible to infection with microbial agents. Infections with pathogens during pregnancy can have devastating consequences to both the fetus and his/her mother. These infections are linked with adverse pregnancy outcomes. Infections with parasites, viruses, or bacteria can be associated with maternal anemia, abortion, intrauterine growth retardation, preterm delivery, fetal morbidity and high risk of mortality during the first years of life. Despite these significant consequences and complications associated with infections by microbial pathogens during the course of gestation, very little is known about the underlying mechanisms of the pathogenesis and immunopathology of infections during pregnancy. The Research Topic proposed here in, will focus on microbial infections during pregnancy. Studies and review papers addressing the pregnant host/fetus/pathogen interactions, the host/fetus immunological response against infections during gestation, trans-placental transfer of infections during pregnancy are welcome. Topics related to model systems used to mirror the biology in human, the pathogenesis and molecular pathways as well as the mechanisms of the disease at the maternofetal interface including the placenta, the amniotic fluid, and the fetal membranes will be considered making the scope and interest of the topic relatively broad. There is a growing number of pathogens associated with pregnancy. In most cases, women are more susceptible to infections with these pathogens when they become pregnant in comparison to their non-pregnant counterparts. Unfortunately, vertical transmission occurs in most cases but the underlying mechanisms are still unknown. The placenta has always been considered as a barrier against congenital infections but studies have indicated that microbial pathogens breach this barrier. The amniotic fluid, and the fetal membranes are also important components of vertical transmission because of their non-sterile state even in most healthy pregnancies. During pregnancy, infections by malaria or toxoplasmosis as well as other viral or bacterial pathogens lead to an uncontrolled inflammatory response recognized as a significant cause for preterm delivery and intra uterine growth retardation leading to low birth weight, a risk factor to infant morbidity and mortality. To successfully prevent, treat, eradicate or educate about microbial infections during pregnancy, we must understand the molecular mechanisms by which they cause poor birth outcomes including how vertical transmission occurs at the maternofetal interface.