1 Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, 505 Parnassus Ave., Box 0132, San Francisco, CA 94143. Electronic address: rosensteinm@obgyn.ucsf.edu.
2 Departments of Epidemiology and Biostatistics and of Pediatrics, University of California, San Francisco, San Francisco, CA.
3 Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, San Francisco, CA.