Mother-to-child transmission of toxoplasmosis: risk estimates for clinicalcounselling

Background. Women who acquire toxoplasmosis infection during pregnancy (in most cases detected through serological screening) require counselling abou t the risk of congenital infection and its clinical sequelae, Reliable esti mates of risk are not currently available, We undertook an analysis of data from women referred to the toxoplasmosis reference laboratory, Lyon, Franc e, between 1987 and 1995. Methods. Information was collected from clinical notes kept at the laborato ry and, where necessary, from the relevant obstetrician or paediatrician vi a telephone. Methods were developed to derive estimates of the risk of cong enital toxoplasmosis by exact duration of gestation at maternal seroconvers ion. Findings. We analysed obstetric and paediatric data on 603 confirmed matern al toxoplasmosis infections. At least 564 women received antiparasitic drug s according to a standard protocol. Congenital infection status was ascerta ined in 554 cases, and infected children were followed-up for a median of 5 4 months. The overall maternal-fetal transmission rate was 29% (95% CI 25-3 3), which masked a sharp increase in risk with duration of gestation from 6 % at 13 weeks to 72% at 36 weeks. However, fetuses infected in early pregna ncy were much more likely to show clinical signs of infection. These effect s counterbalance, and women who seroconverted at 24-30 weeks of gestation c arried the highest risk (10%) of having a congenitally infected child with early clinical signs who was thus at risk of long-term complications. Interpretation. This information will assist the clinical counselling of pr egnant women diagnosed with acute toxoplasmosis and may guide individual de cisions on investigative and therapeutic options. Further studies are requi red to determine the long-term risks of clinical symptoms and disability du e to congenital toxoplasmosis.