Reactivation of human herpesvirus 6 during pregnancy

Reactivation of human herpesvirus 6 (HHV-6) and cytomegalovirus (CMV) durin g pregnancy and transmission of the viruses to the fetus were investigated by polymerase chain reaction (PCR) and serology, In all, 104 blood samples were obtained 3 times during pregnancy and once at delivery. In another 107 women, samples were obtained only at delivery. Cord blood samples were obt ained from both groups of women. HHV-6 DNA was detected in 41%-44% of the s amples during months 3-8 of pregnancy, in 25% at delivery, and in 24% of ag e-matched controls. HHV-6 DNA was found in 1.0% of the cord blood samples. CMV DNA was detected in 1.7% of leukocytes from 104 pregnant women but in n o cord blood sample. IgG antibodies to HHV-6 were found in 96% and CMV IgG in 62.5% of the women. HHV-6 IgG titers were significantly higher in HHV-6 PCR-positive women. Thus, HHV-6 reactivation seems common during pregnancy, and transfer of HHV-6 to the fetus may occur in similar to 1% of pregnanci es.