What is the chance that an HCV infected women will spread HCV to their newborn infants?

Small. If there is no active bleeding wounds, the chances are small. The cdc and american academy of pediatrics do not contraindicate the breastfeeding in mothers, who are the carrier for the hcv.
Negligable. Transmisson of hepatitis C from person to persion via casual contact is rare. Transmission via nursing has not been reported. Generally hepatitis C is transmited via blood to blood contact (tainted blood transfusion, needle sticks from tainted needles, IV drug use with needle sharing, etc,).