Effect of timing and type of treatment on the risk of mother to child transmission of Toxoplasma gondii

Objective: To determine the effects on mother to child transmission of the timing and type of prenatal treatment, taking into account gestational age at maternal seroconversion. Design: Prospective cohort study. Setting: European centres offering prenatal screening for toxoplasmosis. Population: Children born to a cohort of pregnant women with toxoplasma infection. Methods: We determined the effects on mother to child transmission of the interval between seroconversion and start of treatment (treatment delay), and the type of treatment, taking into account gestational age at maternal seroconversion. Main outcome measure: Congenital infection status confirmed by toxoplasma IgG results at one year postnatal age. Results: Of 1208 women analysed, 72% were first prescribed spiramycin, 19% pyrimethamine-sulphonamide and 9% (mostly infected during the last trimester) were untreated. The odds ratios for mother to child transmission for all women treated after a delay of four to seven weeks was 0.77 (95% CI 0.34-1.69), and after eight weeks or more was 1.33 (0.56-2.89) compared with less than four weeks. The odds ratio per week of treatment delay was 1.01 (0.93-1.08). There was no evidence that transmission risk differed in women first treated with pyrimethamine-sulphonamide versus spiramycin: odds ratio 1.10 (0.63-1.91) or in untreated versus treated women: odds ratio 0.57 (0.27-1.17). Conclusion: We were unable to demonstrate a beneficial effect of the timing or type of prenatal treatment on the risk of mother to child transmission but we could not exclude a clinically important effect. Randomised controlled trials are required to determine the effect of prenatal treatment on mother to child transmission.