Analysis of risk factors for mother-to-infant transmission of HCV. Discussion – Part 2
Evidence for the significance of labor-associated factors for the transmission of blood-borne pathogens was already found in investigations of vertical HIV transmission in twin births. First-born twins were more likely to be infected with HIV-1 than their second-born siblings, especially when the former was of greater birth weight. It was suggested in these studies that the first-born twin would have dilated and, to some extent, mechanically cleansed the birth canal, thereby reducing the duration of exposure of the second twin and, consequently, the risk of transmission
Nevertheless, these observations on the transmission of HCV or HIV represent only indirect evidence for an increased risk in vaginal deliveries with prolonged passage through the birth canal. Data on the exact time required for passage of the birth canal, however, are not routinely recorded during delivery and will have to be collected in future prospective clinical trials
Results of studies on HIV infection as a risk factor for vertical HCV transmission also have been ambiguous. Nevertheless, HIV-HCV coinfection reportedly accelerates HCV disease progression by increasing HCV load, and a higher HCV load in HCV-HIV–coinfected patients may be explained by the observed inverse relation between baseline CD4+ cell count and HCV load. In addition, the risk for transmission is exceedingly low in women who are HIV-HCV coinfected but who have little or no detectable HCV RNA. Consequently, we propose that the more important predictive factor for HCV transmission is very likely HCV load, and not HIV coinfection. In the present study, which included only a small number of HIV-HCV–coinfected mothers, no increased risk for vertical HCV transmission was observed in mothers with HIV coinfection. This finding may be explained by the fact that HCV load in our group of HIV-HCV–coinfected mothers did not significantly differ from that in HIV-uninfected mothers.
Reported average mother-to-infant transmission rates of HCV are 5%–10%; we observed a somewhat higher transmission rate of 12%. However, because of the retrospective design of the present study and the fact that HCV infection status could not be assessed for all children, a selection bias cannot be excluded for this parameter. In addition, our laboratory is the major reference laboratory for the geographic region covered by this study; therefore, preselection of patients possibly occurred
In conclusion, vaginal delivery itself does not appear to be a significant risk factor for mother-to-infant transmission of HCV, but the risk of transmission increased with increasing maternal HCV load and with the occurrence of infantile hypoxia or vaginal or perineal lacerations during vaginal delivery. Although it would be premature to recommend routine cesarean section for HCV-infected women, elective cesarean section may reduce the risk of vertical transmission of HCV among mothers with high HCV viremia, those who are at risk for birth injuries during vaginal delivery, or those whose children are at risk for intrapartum hypoxia