1. Department of Obstetrics and Gynaecology, University of Helsinki, Helsinki University Hospital, Helsinki, Finland;
2. Department of Oral and Maxillofacial Diseases, University of Helsinki, Helsinki University Hospital, Helsinki, Finland;
3. Division of Periodontology, Department of Dental Medicine, Karolinska Institute, Huddinge, Sweden;
4. Medix Biochemica, Espoo, Finland