Congenital toxoplasmosis in twins: a series of 14 pairs of twins: absence of infection in one twin in two pairs.

Fourteen pairs of twins with congenital toxoplasmosis were observed. In two pairs, one twin was infected and had symptoms of chorioretinitis or encephalomyelitis, while the other had a negative dye test upon repeated examination: this phenomenon has not previously been reported. In three of the other twelve pairs of twins, one of each pair died; two of them had evidence of toxoplasmosis; in the cotwin the diagnosis was based on serologic data. Clincial and biologic follow-up extended from 19 months to 8 years in five pairs. Marked discrepancies in the individual clinical patterns of the two children in each of six sets of twins were observed, with evidence of infection in one twin and subclinical infection in the other. These clinical findings correlated well with serologic data in the children in whom sufficient follow-up was permitted. The clinical pattern of congenital toxoplasmosis in twins is extremely similar in monochorial pregnancies, but discrepancies are almost the rule in bichorial pregnancies. The importance of placental lesions in determining the extent of fetal involvement is well illustrated by studies of toxoplasmosis in twins.