An ARM is performed by the caregiver using an 'amnihook'. This is a long, thin implement with a small hook on the end (similar to a crochet hook). The caregiver performs an internal vaginal examination with their fingers, and locates the opening of the cervix. If the woman has dilated to a degree, then this should not be difficult. The caregiver leaves their fingers in place, and then slides the amnihook in, (the hook faces their hand and fingers, so it does 'scratch' the woman's vagina on the way in).
Once the end of the amnihook is in contact with the bag of waters (or the amniotic membrane), the caregiver turns the hook over and attempts to 'snag' the membrane to make a hole. This may be immediate, or take a little while if the membrane is very smooth, or particularly tough. Once the membrane is punctured, some of the amniotic fluid should be released.
Image 4-35 shows an amnihook compared to a ballpoint pen to illustrate the length of the amnihook.
Image 4-36 of shows the hooked end of the amnihook that breaks the membranes.
After the hole is made in the membrane, the amnihook is removed (again sliding it out hook with the towards their hand). The caregiver may then use their fingers to try and tear the hole in the membrane (to open it further). At this point, the woman usually feels a large gush of warm fluid. Opening the hole further ensures that the hole does not 'close over' again. This is sometimes possible because the membrane is made up of 2 layers. If the hole is small, the 2 layers can slide back over each other, sealing off the opening. If this happens, the ARM may need to be repeated again, usually a little later when it is realised that no fluid is continuing to drain away.
Once the waters are broken, the caregiver listens to the baby's heart rate for a minute or two, by using a hand held
Doppler or a
Pinard's fetal stethoscope.