1 Division of Epidemiology and Clinical Research, Department of Pediatrics, University of Minnesota Medical School, Minneapolis.
2 Division of Pediatric Hematology/Oncology, Department of Pediatrics, University of Minnesota Medical School, Minneapolis.
3 Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Diego.