1. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California, Irvine, Orange, California.
2. Obstetrics and Gynecology, American College of Obstetricians and Gynecologists, Washington, District of Columbia.
3. Center for Statistical Consulting, University of California, Irvine, Orange, California.
4. Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, Utah.