1. Division of Research, Kaiser Permanente Northern California, Oakland, California
2. Department of Obstetrics and Gynecology, The Permanente Medical Group, Oakland, California
3. Department of Obstetrics and Gynecology, INOVA Medical Group-Cares, Falls Church, Virginia
4. Department of Maternal Fetal Medicine, The Permanente Medical Group, Kaiser Permanente Northern California, Walnut Creek, California