Detectable Trypanosoma cruzi parasitemia during pregnancy and delivery as a risk factor for congenital Chagas disease.

Vector control has led to a drastic decrease in the prevalence of acquired Chagas disease in Latin America, thus redirecting attention to congenital Chagas disease. We report results of a longitudinal study of 359 pregnant women in Yacuiba in southern Bolivia, of whom 147 (40.9%) were infected with Trypanosoma cruzi, to evaluate the relationship between the patency period of the parasitemia and the risk of congenital infection. Maternal infection was assessed by using T. cruzi-specific serologic tests, and parasitemia in mothers and newborns was diagnosed by using microscopic examination of blood in heparinized microhematocrit tubes. Parasitemia was present in 28.6% of the infected women. Its prevalence increased during the third trimester, then decreased at delivery. The likelihood of congenital infection was significantly correlated with the parasite density in the mother's blood. The risk of transmission increased during the third trimester of pregnancy and could explain premature births or low-weight newborns for infected mothers.