According to the Cerebral Palsy Outreach Network, twins and other multiples are about four times more likely than single birth children to be affected by the disease, a neurological disorder that impairs muscle coordination. Here, Rye, NY, mom Janet Farrell Leontiou, 59, a professor of communications and author of the book " What Do the Doctors Say? ," tells The Post's JANE RIDLEY why she believes in vitro fertilization played a part in creating her son's disability.