AdvertisementGetting To The Core Of Exercises Said To Strengthen 'Mum Tum'August 20, 2017Michaeleen DouclefffacebookEmailVanessa Wauchope begins abdominal exercises in Leah Keller's class in San Francisco, Calif. Keller teaches an exercise, called "drawing in," to help strengthen abdominal muscles that tend to spread apart a bit during pregnancy. (Talia Herman for NPR)