Toxoplasma Transmission to the Fetus during the Periconceptional Period.

In Tunisia, toxoplasmosis screening in pregnancy is common but not regulated. This study evaluated congenital toxoplasmosis after primary infections during the periconceptional period and the accuracy of diagnostic tools. We analyzed 209 women at the Pasteur Institute of Tunis (2005-2021) with primary infections classified as periconceptional (n = 50, 23.9%), first trimester (n = 121, 57.9%), or second trimester (n = 38, 18.2%). Congenital toxoplasmosis was confirmed in 29 cases (13.9%), diagnosed prenatally in 22 cases, and diagnosed postnatally in 7 cases. Transmission rates were 14%, 8.2%, and 31.5% for periconceptional, first-trimester, and second-trimester infections, respectively, with significantly higher transmission in the second trimester (P = 0.048 versus periconceptional, P = 0.0003 versus first trimester). Prenatal diagnosis was positive in 42.8% of cases during the periconceptional period, 90% of cases during the first trimester, and 83.3% of cases during the second trimester, with false-negative polymerase chain reactions being more frequent during the periconceptional period (P <0.05). Periconceptional infections pose a high risk of fetal transmission, requiring monitoring.