Analysis of risk factors for mother-to-infant transmission of HCV. Discussion
Vertical transmission from infected mothers has become the most important mode of HCV infection among children. Although numerous studies have addressed this issue, the mechanisms of vertical HCV transmission, including the timing of infection, remain largely unknown.
It is generally agreed that the risk of vertical HCV infection in mothers without detectable HCV viremia is exceedingly low. We also found HCV viremia to be a prerequisite for transmission, because none of the HCV RNA–negative mothers transmitted the virus to her child.
However, there is no general consensus that the risk of transmission is higher in mothers with high HCV load than in mothers with low HCV load. In the present study, the mean maternal HCV load was higher in mothers whose children were HCV infected than in those whose children were not infected, but high viremia was not a statistically significant risk factor for transmission. However, when we included the mode of delivery into our analysis, it became apparent that, in the case of a vaginal delivery, this difference in mean virus load was even more pronounced. In addition, except for 1 HIV-HCV–coinfected woman, none of the 23 mothers who had a cesarean section transmitted HCV to her offspring
Previous reports found strong evidence that mother-to-child transmission rates and substantial intrapartum transmission of HCV may possibly be reduced by elective cesarean delivery. However, some studies were criticized for testing only a minority of women for HCV RNA and for not addressing possible mechanisms involved in the reduction of vertical transmission of HCV by elective cesarean section. We not only tested 97% of the mothers for HCV RNA but also identified factors that may increase the risk of HCV transmission in vaginal deliveries.
We observed a significantly increased risk of HCV infection in children with a low umbilical cord–blood pH, which is indicative of infantile hypoxia. Whether this intrapartum hypoxia may have led to aspiration of HCV-contaminated maternal fluids or to other hypoxia-related mechanisms of virus transmission can only be speculated.
Moreover, a significantly increased risk of mother-to-infant transmission of HCV was observed in the case of leakage of maternal blood into the birth canal by tears of the cervix or vagina. In contrast, when an episiotomy, which also is associated with maternal bleeding, was performed, it did not increase the risk for vertical transmission of HCV. This apparent contradiction may suggest a more extensive, and possibly longer, exposure of children to virus-contaminated maternal fluids during vaginal deliveries that involve vaginal or perineal lacerations than during those that involve an episiotomy. Although it may be theorized that passage through the birth canal may be prolonged in mothers with relatively large children or that, in women with vaginal or cervical tears, the canal first had to be dilated by the child before passing through it, which allowed for more extensive exposure to virus-contaminated maternal blood, these details will have to be elucidated in prospective clinical trials. Still, since an episiotomy is, in general, performed at the end of labor, intrapartum exposure to maternal blood is very likely shorter in this incidence than in the case of vaginal or perineal lacerations.