SKJAERVEN, ROLV; IRGENS, LORENTZ M.; LIE, ROLV T.; SKJAERVEN ROLV; Section for Medical Information and Statistics, University of Bergen; Medical Birth Registry of Norway, University of Bergen, MFH Building 5021 Bergen Norway, University of Bergen; IRGENS LORENTZ M.; Medical Birth Registry of Norway, University of Bergen, MFH Building 5021 Bergen Norway, University of Bergen; LIE ROLV T.; Medical Birth Registry of Norway, University of Bergen, MFH Building 5021 Bergen Norway, University of Bergen