[1] UNIV BERGEN,DEPT OBSTET & GYNECOL,N-5014 BERGEN,NORWAY
[2] UNIV BERGEN,DEPT PEDIAT,N-5014 BERGEN,NORWAY
[3] NICHHD,PREVENT RES PROGRAM,BIOMETRY BRANCH,BETHESDA,MD 20205
[4] UNIV TRONDHEIM,DEPT COMMUNITY MED & GEN PRACTICE,TRONDHEIM,NORWAY
[5] UNIV ALABAMA,DEPT OBSTET & GYNECOL,BIRMINGHAM,AL 35294
[6] UNIV UPPSALA,DEPT OBSTET & GYNECOL,S-75105 UPPSALA,SWEDEN