1. Maternal and Fetal Medicine Section Institute of Medical Genetics Yorkhill Glasgow G3 8SJ U.K.
2. Department of Obstetrics and Gynaecology Royal Victoria Infirmary Newcastle upon Tyne NE1 4LP U.K.
3. Department of Obstetrics and Gynecology University of Cincinnati, College of Medicine Cincinnati Ohio 45267 USA
4. Department of Pathology Royal Victoria Infirmary Newcastle upon Tyne NE1 4LP U.K.