Blame It on Biology
All female mammals begin preparing their surroundings for a newborn in advance of its birth -- and humans are no exception. "It's nature's way of ensuring that the environment we bring a child into will be safe, warm, and welcoming," says Parents advisor Hilda Hutcherson, MD, clinical professor of obstetrics and gynecology at Columbia University, in New York City. No one knows exactly what prompts the behavior, but experts suspect that hormones play a big role. "During pregnancy, your body produces increasing amounts of oxytocin and prolactin, both of which are thought to be responsible for maternal bonding," says Louann Brizendine, MD, director of the Women's Mood & Hormone Clinic at the University of California at San Francisco and author of The Female Brain. "These hormones reach peak levels in the last month of pregnancy." Other medical experts attribute nesting to a primal instinct that harks back to a time when physical preparation of one's surroundings was necessary for a safer childbirth.