Obstetric factors and mother-to-infant transmission of HIV-1.

Mother-to-infant HIV transmission has been reported to occur during pregnancy (in utero), at delivery, or postpartum (breast feeding). There are a multiplicity of variables or cofactors that may influence such transmission. Among the obstetric factors reported to be more strikingly associated with mother-to-infant transmission are preterm delivery, low birth weight and birth order in twin pregnancies. Perhaps the most controversial issue in obstetric management is the association of mode of delivery and transmission. Some large studies and metaanalyses have found a protective effect of cesarean section varying from odds ratios of 0.8 to 0.56. Unfortunately, those large studies have not included the duration of rupture membranes in their analyses. When such a variable (duration of ruptured membranes) is taken into account, the protective effect of the cesarean section may disappear. The impact of such obstetric variables on transmission can be explained by the hypothesis that a significant proportion of the perinatal transmission occurs intrapartum and is related to the dose exposure (time and concentration) of the presenting part to the genital tract virus load and to the maternal blood virus load. Currently, routine cesarean section is not recommended as a strategy for the prevention of vertical transmission. Although prospective studies are underway to elucidate the effect of cesarean section on transmission, the results are academic if recent potent antiviral agents are demonstrated to reduce or minimize the viral load in blood and in cervicovaginal secretions. Meanwhile, the current management of the delivery process should have as a goal the reduction of the presenting part to the cervicovaginal secretions by preserving the intactness of the membranes and by the proper use of invasive procedures when clinically indicated.