Riggs Margaret A, Klebanoff Mark A
Division of Epidemiology, Statistics and Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
Clin Obstet Gynecol. 2004 Dec;47(4):796-807; discussion 881-2. doi: 10.1097/01.grf.0000141450.61310.81.