Delayed amplification of cytomegalovirus infection in the placenta and maternal tissues during late gestation.

To stimulate first-trimester human cytomegalovirus infection, pregnant guinea pigs were inoculated with a low dose of guinea pig cytomegalovirus during the first trimester of pregnancy. Maternal viremia, which was cleared by 2 weeks after inoculation, was found to reappear near the time of delivery in one third of the animals tested. The virus, first detected in the placenta during initial maternal viremia, replicated after the time when maternal blood was cleared of virus, although high titers of maternal serum antibodies were present. In the last week of gestation (43 to 48 days after inoculation), the virus was detected in 95% of placentas and was present at high titers. Fetal infection first appeared on day 25 after inoculation and reached an incidence of 37% in the last week of gestation despite the presence of fetal antibody. These results suggest that the placenta may amplify cytomegalovirus infection late in human gestation, even after low-dose infection in the first trimester.