To study mother-to-infant transmission of GB virus C/hepatitis G virus (GBV-C/HGV), blood samples of infants born to carrier mothers were collected beginning 3 months after birth and were tested for GBV-C/HGV RNA until 1 year of age. Of 2046 mothers, 2.1% were positive for GBV-C/ HGV RNA, and 25 of their infants were followed for a median of 12 months. Thirteen infants (52%) were viremic, and infection became persistent in all. Maternal GBV-C/HGV RNA levels of this group were ú10 7 copies/mL. Nucleotide sequence comparison in 5 viremic mother-infant pairs revealed a homology of 93% -98.2%, and none delivered by elective cesarean section. In comparison, of the 12 uninfected infants' mothers, 10 had lower GBV-C/HGV RNA levels (mean, 5 1 10 4 copies/ mL), and the remaining 2 high-titered mothers had elective cesarean section. Thus, high-titered maternal viremia and mode of delivery are closely associated with the mother-to-infant transmission of GBV-C/HGV to infants, and the infection usually becomes persistent. for GBV-C/HGV RNA and alanine aminotransferase (ALT) startcan also be found in patients with community-acquired hepatiing from 3 months after birth until 1 year of age (usually every tis [14] and is distributed worldwide, with a higher prevalence 2-3 months). The infected neonates and blood sampling times are in certain risk groups [9 -15].shown in figure 1. The duration of follow-up was comparable between infected and uninfected infants. Although perinatal transmission of GBV-C/HGV has beenThe mode of delivery was classified into elective cesarean reported to occur in some instances [16 -18], the case number section, emergent cesarean section, and normal spontaneous delivis small, and thus the prevalence, risk factors, and significance ery [20]. remain unclear. We therefore investigated the frequency of Materials and Methodsrum GBV-C/HGV RNA was detected by reverse transcriptionSubjects. Serum samples of 2046 consecutive pregnant women polymerase chain reaction (RT-PCR) with primers from the 5-collected from May 1995 to May 1996 and stored at 020ЊC were untranslated region of the viral genome [21], and the positive maternal serum samples were further quantified. To screen the GBV-C/HGV genome, serum specimens from 10 pregnant women were pooled and then subjected to 21]. In case