The Memory Keeper's Daughter by Kim Edwards

But for a blizzard on the night that Norah Henry gave birth to twins, many lives would have been different. Norah’s surgeon husband, David, delivers the babes, a healthy boy and Phoebe, who has Down’s syndrome. Appalled, he begs nurse Caroline Gill to take the tiny girl to an institution and leave her there, telling Norah that the baby died. Caroline, unwilling to abandon Phoebe, raises her as her own. Not until Phoebe is an adult does Norah learn that her daughter did not die. A remarkable story of how lives may be changed by the simple falling of snow.