Two recently published studies demonstrate that the risk of transmission of hepatitis C from mother to infant is increased by concomitant HIV infection, but unlike HIV, the risk of vertical transmission of hepatitis C is not reduced by elective cesarean section.
Additionally, the larger of the two studies turned up the surprising result that girl babies are at twice the risk of vertical transmission as are boys (J. Infect. Dis. 2005;192:1872–9).
That study, by the European Paediatric Hepatitis C Virus Network, involved 1,479 pregnant women with confirmed hepatitis C infections from 33 sites across Europe. They and their babies were followed prospectively over at least 24 months.
Infants were counted as being infected only if they tested positive (by an RNA polymerase chain reaction test and/or by the presence of anti-hepatitis C antibodies) after the age of 18 months. This is the age by which passively acquired maternal antibodies have almost always disappeared.
The overall hepatitis C vertical transmission rate was 6.2%. Among mothers who were coinfected with HIV, the transmission rate was 8.7%, significantly higher than the 5.5% rate seen among mothers who were infected only with hepatitis C.
After adjusting for maternal HIV infection status, mode of delivery, prematurity, and infant feeding type, the study showed that female infants had 2.07 times the risk of vertical transmission as males, a statistically significant increase.
In this study, a number of factors showed no significant association with vertical transmission.
Among them were whether the mothers had a history of intravenous drug use, whether they were using such drugs during pregnancy, the mode of delivery (vaginal vs. elective cesarean section vs. emergency cesarean section), and whether the infant was taking formula or was breast-fed.
The second study by Eric E. Mast, M.D., of the Centers for Disease Control and Prevention, Atlanta, and his colleagues analyzed 242 women who were confirmed as positive for hepatitis C during pregnancy and their 244 live-born infants (J. Infect. Dis. 2005;192:1880–9).
The overall vertical transmission rate in this study was 3.7%. Women who were coinfected with HIV were 6.5 times more likely to transmit hepatitis C than those who were not coinfected.
Among the HIV-negative women, vertical hepatitis C transmission was significantly associated with several factors, including membrane rupture more than 6 hours before delivery and the use of internal fetal monitoring devices.
The investigators concluded that avoiding internal fetal monitoring and/or performing a cesarean section before or soon after membrane rupture could decrease the risk of vertical hepatitis C transmission.
Some infants who turned out ultimately to be uninfected with hepatitis C nevertheless tested positive for anti-hepatitis C antibodies as late as 15 months following birth, a result of passively acquired maternal antibodies.
The investigators recommended that infants be tested after the age of 18 months to avoid false-positive results.
In this study, vertical transmission occurred in six girls, compared with three boys, but the small sample size prevented this difference from reaching statistical significance.