A significant risk associated with velamentous cord insertion is:

Velamentous cord insertion involves the umbilical cord attaching to the membranes rather than directly to the placenta. This presents a significant risk of fetal hemorrhage, particularly during labor and delivery. The vessels, which are not protected by Wharton's jelly, can be easily torn when membranes rupture or during contractions. If a vessel is ruptured, it can lead to rapid fetal blood loss, significantly compromising the fetus's blood supply and oxygenation.

In contrast, the other options present risks that are either less directly related to this condition or are not the main concern. For instance, infection can occur in various obstetric scenarios but is not a hallmark risk specifically associated with velamentous cord insertion. Maternal hemorrhage, while a potential concern in numerous childbirth complications, is less relevant to this specific insertion scenario. Preterm labor can be influenced by various factors, but it is not a direct consequence of a velamentous cord insertion.