[1] Georgia Perinatal Consultants, Atlanta, GA 30309 USA
[2] Kaiser Permanente Southern Calif, Dept Obstet & Gynecol, Downey, CA USA
[3] Montefiore Med Ctr, Albert Einstein Coll Med, Dept Obstet & Gynecol & Womens Hlth, Bronx, NY 10467 USA
[4] Montefiore Med Ctr, Albert Einstein Coll Med, Dept Epidemiol & Populat Hlth, Bronx, NY 10467 USA
[5] NYU, Dept Anesthesia, New York, NY USA