Perinatal transmission of hepatitis C virus from mother to infant has been well-documented; however, reports about the risk of infection vary widely, ranging from zero to 100 percent. Transmission of hepatitis C virus may occur in utero, at the time of delivery and through breast-feeding, all of which are identical to the modes of transmission for human immunodeficiency virus (HIV) infection. In fact, several studies have reported a higher incidence of hepatitis C virus transmission by mothers with HIV coinfection, although these results are somewhat controversial. Tovo and colleagues attempted to quantify the risk of infection by evaluating the incidence of hepatitis C virus transmission in infants born to mothers with or without HIV coinfection. Other potential factors for transmission were also investigated, including the progression of maternal HIV, a history of intravenous (IV) drug use, the length of the pregnancy, infant birth weight, mode of delivery and type of infant feeding.

A total of 245 singleton at-risk infants born to mothers who were positive for hepatitis C virus were enrolled in the study two weeks after birth and were followed for at least 18 months. Maternal data collected included risk factors for hepatitis C virus infection (i.e., IV drug use, history of transfusion, infected partner), HIV status, length of pregnancy, mode of delivery, infant birth weight and type of feeding. Baseline infant data included the presence of HIV and hepatitis C virus antibodies at birth. All 245 children were seen every three to five months, for up to 18 months after birth. At each visit, hepatitis C virus and HIV testing was repeated, including determination of hepatitis C virus RNA levels.

After 18 months, only the children who remained positive for hepatitis C virus and/or HIV were followed, since they were considered to be infected and no longer carriers of maternal antibody. These children were followed for an additional mean period of 28 months. To further assess the impact of maternal HIV infection on hepatitis C virus transmission, the children were divided into two groups. Group A included children of women with hepatitis C virus only, and group B included children of women with hepatitis C virus and HIV coinfection.

Twenty-eight children (11.4 percent) became infected with hepatitis C virus, including 3.7 percent (three of 80) from group A and 15.1 percent (25 of 165) from group B. Of the children in group B, 22 (13.3 percent) acquired HIV, including six children who were coinfected with hepatitis C virus.

Overall, children delivered vaginally were more often infected with hepatitis C virus (13.9 percent) than those delivered by cesarean section (5.6 percent). A similar pattern was seen for HIV infection, in which children delivered vaginally (16.8 percent) had a higher risk for infection than those delivered by cesarean section (4.3 percent). The presence of HIV-related symptoms in the mother was not associated with an increased risk of hepatitis C virus or HIV transmission. Similarly, maternal IV drug use, premature delivery and low birth weight did not affect the risk of hepatitis C virus transmission. Infants in group B were bottle-fed. Infants in group A who were breast-fed showed no increased risk for hepatitis C virus infection.

The authors concluded that vertical transmission of hepatitis C virus is uncommon, which supports other studies that found that maternal HIV coinfection significantly increases the risk of hepatitis C virus infection in an infant. Infants exposed perinatally usually clear maternal hepatitis C virus-IgG antibody by six to 12 months of age, although some have persistent maternal antibody for up to 18 months. Thus, these infants cannot be considered infected before 18 months when tested by conventional serologic methods only. Delivery by cesarean section appears to decrease the risk of hepatitis C virus transmission, suggesting that most infants become infected at the time of delivery and are not infected in utero. The authors further state that mothers with hepatitis C virus should not be discouraged from breast-feeding, since transmission through lactation is unlikely.