1. Department of Obstetrics and Gynaecology, University of Manchester, St Mary's Hospital, Manchester M13 0JH, U.K.
2. Department of Pathological Sciences, University of Manchester, St Mary's Hospital, Manchester M13 0JH, U.K.
3. Instituto Chileno de Medicina Reproductiva, Santiago, Chile
4. Department of Obstetrics and Gynecology, University of Illinois, Chicago, IL 60612, U.S.A.