Induction – artificial rupture of membranes

This is the fourth article in our short series of articles discussing the most common methods of induction. Each of the articles is aimed at being read in 3 minutes or less. In this article, we cover the artificial rupture of membranes.

Artificial rupture of membranes (ARM)

ARM, breaking your waters or amniotomy is the procedure used to rupture your amniotic sac.

The procedure involves inserting a crochet hook like instrument (amnihook or amnicot) into your vagina to make a small opening in the amniotic sac. Occasionally, the midwife accidentally breaks your waters during a vaginal examination.

Why would you need an ARM?

Your caregiver is likely to suggest breaking your waters if:

  • your membranes are physically accessible to your caregiver,
  • you are over 41+ weeks, and your labour hasn’t commenced*,
  • the baby isn’t descending into the birth canal,
  • your labour has stalled, or
  • your caregivers need to attach foetal monitoring devices to the baby’s scalp.

What happens first

Before undertaking this procedure, your caregiver will perform a vaginal examination, checking:

  • that there is no reason your caregiver should not perform the procedure,
  • the progress of your cervical dilation,
  • your baby’s presentation, station and position, and
  • that the opening of the cervix is clear (no vasa praevia or cord presentation).


Risks associated with an amniotomy are:

  • infection,
  • foetal compromise,
  • cord prolapse, where there is a very small risk of the umbilical cord slipping below the baby’s head, or
  • an accidental rupture of a vasa praevia.

When you can’t have an ARM

Your caregiver is unlikely to suggest an ARM in the following circumstances:

  • there is a suspicion of a low lying placenta, placenta praevia or vasa praevia,
  • you have HIV or active herpes lesions, or
  • if your baby is in the traverse position.

After the procedure, your caregiver will check the colour, quantity, odour and consistency of your amniotic fluid.  She will also assess your babies heart rate.

* Unfortunately, there is limited evidence to suggest ARM alone can induce labour if you have an unfavourable cervix.


Next in our series is Oxytocin Infusion.

This blog post is general in nature.  Please do not treat this blog as medical advice – it is not.

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