1. Department of Obstetrics & Gynaecology, Atrium Medical Centre Parkstad, Heerlen, The Netherlands,
2. St. Elisabeth Hospital, Willemstad, Curacao,
3. Department of Statistics, Atrium Medical Centre Parkstad, Heerlen, The Netherlands, and
4. Department of Pediatrics, Atrium Medical Centre Parkstad, Heerlen, The Netherlands