1. Clinical and Molecular Genetics Unit UCL Institute of Child Health London UK
2. Fetal Medicine Unit University College London Hospitals NHS Foundation Trust London UK
3. North East Thames Regional Genetics Laboratory Great Ormond Street Hospital London UK
4. Fetal Medicine Unit Academic Medical Centre Amsterdam The Netherlands
5. Department of Obstetrics and Gynaecology West Herts Hospital Watford Hertfordshire UK
6. Paediatric Epidemiology and Biostatistics UCL Institute of Health London UK