1. From the Department of Clinical Epidemiology (A.v.H.V., F.M.H., and F.R.R.), Leiden University Medical Center, Leiden, the Netherlands; the Department of Gynaecology and Reproductive Medicine (F.M.H.), Leiden University Medical Center, Leiden, the Netherlands; the Thrombosis and Haemostasis Research Center (F.R.R.), Leiden University Medical Center, Leiden, the Netherlands; and Einthoven Laboratory for Experimental Vascular Medicine (F.R.R.), Leiden University Medical Center, Leiden, the Netherlands.