1. Department of Epidemiology and Biostatistics, School of Public Health Indiana University Bloomington Bloomington Indiana USA
2. Department of Obstetrics and Gynecology Columbia University Irving Medical Center New York City New York USA
3. Department of Epidemiology Columbia University Irving Medical Center New York City New York USA
4. Department of Obstetrics and Gynecology Mount Sinai West Hospital New York City New York USA