1. Maternal and Fetal Medicine SectionInstitute of Medical Genetics Yorkhill Glasgow G3 8SJ U.K.
2. Department of Obstetrics and GynecologyUniversity of CincinnatiCollege of Medicine Cincinnati Ohio 45267–0526 USA
3. Department of Pathology Newcastle upon Tyne NE1 4LP U.K.
4. Department of Obstetrics and GynaecologyUniversity of Newcastle upon TyneRoyal Victoria Infirmary Newcastle upon Tyne NE1 4LP U.K.