To evaluate the association between treatment and mother-to-child transmission of acute Toxoplasma gondii infection in pregnancy. This was a concurrent cohort study of 26 pregnant women diagnosed with acute toxoplasmosis. Transmission of T. gondii to the fetus was characterized by detection of the parasite in the amniotic fluid by polymerase chain reaction (PCR). Congenital toxoplasmosis was diagnosed by a positive serological test for IgM, intracranial calcification, chorioretinitis, hydrocephalus, and/or microcephaly in the newborn. There was direct correlation between acute toxoplasmosis and low socioeconomic status and inadequate hygienic/health conditions. The MCT rate in adequately and inadequately treated patients was 17.4% and 33.3%, respectively. PCR analysis of the amniotic fluid was performed for 15 women, with 1 positive result; the pregnant woman was adequately treated, and her infant had no complications. Congenital infection occurred in 4 newborns, who had hydrocephalus, intracranial calcifications, and chorioretinitis. Cerebrospinal fluid alteration was found in 3 of the 16 infants tested. Transmission was more frequent in the third quarter of pregnancy (P = 0.04). The rate of mother-to-child transmission of T. gondii is higher in untreated pregnant women and those who acquired the infection later in pregnancy.