1. Department of Obstetrics, Maternal-Foetal Medicine Unit; Vall d'Hebron University Hospital, Universitat Autònoma de Barcelona; Barcelona Spain
2. Spanish Maternal and Child Health Network Retic (SAMID); Instituto de Salud Carlos III; Madrid Spain
3. Department of Obstetrics; Hospital Universitario Materno-Infantil de Las Palmas de Gran Canaria; Las Palmas de Gran Canaria Spain
4. Department of Obstetrics; BCNnatal, Hospital Sant Joan de Dèu; Barcelona Spain
5. Department of Obstetrics; Hospital Son Llatzer, Palma de Mallorca; Spain
6. Department of Statistics and Preventive Medicine; Vall d'Hebron University Hospital, Universitat Autònoma de Barcelona; Barcelona Spain