Cytomegalovirus (CMV) can infect a fetus even if the mother has had remote infection before pregnancy. However, it is not known whether maternal CMV immunity reduces the risk of transplacental infection. Fowler and colleagues compared rates of congenital infection according to maternal serologic status before pregnancy.

The authors studied the records of 3,461 parturients who had at least one other delivery at the study hospital and whose previous offspring's cord serum specimens were available. Cord serum specimens from current and previous pregnancies were compared to determine seroconversion. Newborns were screened for congenital CMV infection.

At the time of the previous pregnancy, 2,857 (82.5 percent) of the mothers had CMV antibodies, and 604 (17.5 percent) were seronegative. Congenital CMV infection occurred in 46 infants (1.3 percent) of all the study mothers, with 18 (3 percent) occurring in seronegative mothers and 29 (1 percent) occurring in immune mothers. Of all the congenital CMV infections in the initially seronegative group, 142 mothers (23.5 percent) seroconverted between pregnancies. Multivariate analysis, controlling for immune status at previous birth, age, race, insurance status, and gravidity, indicated that older maternal age (25 years or older) and maternal immunity were strongly associated with reduced risk of congenital CMV infection.

The authors conclude that young women who have immunity to CMV from naturally acquired infection are 69 percent less likely to give birth to an infant with congenital CMV infection than are those who are initially CMV seronegative. Risk for congenital CMV was particularly high in mothers who seroconverted in the average three-year interval between pregnancies.

This study provides an estimated CMV infection rate in the offspring of immune mothers of 1 percent. Remote immunity appears to have a protective effect, which suggests that a vaccine would reduce congenital CMV infection rates. In addition, because of the association between younger age and congenital CMV infection, postponing pregnancy until the woman is at least 20 years old could also reduce congenital CMV infection rates.