1 Department of Obstetrics and Gynecology, PEDEGO Research Unit, Medical Research Center Oulu, University Hospital of Oulu and University of Oulu, Oulu, Finland.
2 National Institute for Health and Welfare, Oulu, Finland.
3 Department of Obstetrics and Gynecology, University of Helsinki and Kätilöopisto Hospital, Helsinki University Hospital, Helsinki, Finland.
4 National Institute for Health and Welfare, Helsinki, Finland and Karolinska Institutet, Stockholm, Sweden.