Primary and secondary maternal cytomegalovirus infections and their relation to congenital infection. Analysis of maternal sera.

4 382 new mothers were examined retrospectively with the enzyme-linked immunosorbent assay (ELISA) for IgG activity to cytomegalovirus (CMV) during pregnancy. Some of them were also studied with the indirect immunofluorescence (IIF) test for CMV-IgM antibodies. All the infants had been studied for CMV excretion within the first week of life. Nineteen of them had been shown to be congenitally infected with CMV. 1 218 (28%) women lacked CMV-IgG activity at their first antenatal visit (usually in months III-IV). Fourteen of them seroconverted before parturition (primary infection). Thirteen of the seroconverters were shown to develop CMV-IgM activity. In 6 (43%) cases the primary infection was transmitted to the offspring. The remaining 13 congenitally infected infants were born to mothers with a positive IgM-test at their first antenatal control. Only one of these mothers had a clearly positive IgM-test. She was shown to lack CMV-antibodies before conception (primary infection during the first trimester). Preconceptional sera were obtained from further 4 of the 13 seropositive mothers of congenitally infected infants; all 4 had CMV antibodies before pregnancy (secondary infection during pregnancy). The combined studies of the mothers and infants revealed that 21-63% of the congenital infections could have been caused by secondary maternal infections. Prospectively performed, the study would only have disclosed one of the three fetal CMV infections that resulted in neurological sequelae.