1. Department of Medical Statistics, School of Public Health, Centre of Postgraduate Medical Education, 01-826 Warsaw, Poland
2. First Department of Obstetrics and Gynecology, Centre of Postgraduate Medical Education, 01-004 Warsaw, Poland
3. Saint Sophia Specialist Hospital, 01-004 Warsaw, Poland
4. Department of Midwifery, Centre of Postgraduate Medical Education, 01-004 Warsaw, Poland