Background. Both intrauterine and sexual transmission of human herpesvirus (HHV)-6 and HHV-7 have been suggested, and congenital HHV-6 infection does occur. We prospectively studied HHV-6 and HHV-7 at multiple sites in pregnant women to determine the characteristics of these viruses at repeated time points.

Methods. Peripheral blood mononuclear cells (PBMCs), cervical secretions, placenta, and cord blood were tested by nested polymerase chain reaction (PCR) and reverse-transcriptase PCR for HHV-6 and HHV-7 and by quantitative PCR for HHV-6. A control group of women was also studied.

Results. We enrolled 104 pregnant and 31 control women. HHV-7 DNA was detected more frequently in PBMCs from pregnant women (66.9%) than HHV-6 DNA (22.2%; P < .0001), but both were found at low rates in cervical swabs (HHV-7 vs. HHV-6 DNA, 3.0% vs. 7.5%; P=.19). Pregnant women with HHV-6 DNA present in cervical swabs had a greater odds of having HHV-6 DNA present in the blood than did pregnant women with negative cervical swabs (odds ratio, 12.9; P=.0009). HHV-6 reactivation or reinfection was suggested in 17% of pregnant women. One placental sample had active HHV-6 replication.

Conclusions. Detection of HHV-6 DNA in cervical secretions is associated with HHV-6 DNA in PBMC samples. Active placental infection along with congenital HHV-6 infection was identified.