Pratt dilators: resistance at 9 mm is an instrumentation artifact.
A previous study reported frequent resistance of the cervix at 9 mm during dilation and interpreted the resistance as the beginning of a tear of the internal os. A more recent identical study did not indicate such tears. Measurement of the dilators revealed that the set used in the previous study had uneven increments in diameter with a wide variation between size 25 and size 27 dilators. Increments of newer dilators are more even, and newer dilators reveal a more even progression of cervical resistance with increasing diameter.
Hulka
J F
JF
Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, Chapel Hill 27599-7570.
D000028:Abortion, Induced / Q000295:instrumentation*; D002138:Calibration; D002584:Cervix Uteri; D004106:Dilatation / Q000295:instrumentation; D005260:Female; D006801:Humans