Amniotomy (AROM)

What is an Amniotomy?

Amniotomy is a medical procedure where a healthcare provider intentionally ruptures the amniotic sac surrounding the fetus. This procedure is also known as an “artificial rupture of membranes” (AROM). Rupturing the membranes is thought to release endogenous prostaglandins which in turn may result in cervical changes and spontaneous labour. 

It is most commonly used;

• To induce labour

• Augment labour 

• Facilitate internal monitoring of fetal heart rate and uterine activity 

What is the function of the amniotic sac?

The amniotic sac is a thin, transparent membrane filled with amniotic fluid that surrounds the fetus during pregnancy. 

The purpose of the amniotic sac and amniotic fluid:

• Protects the fetus from injury and infection

• Cushions the fetus and umbilical cord

• Helps regulate the fetus's body temperature

• Helps the fetus's lungs develop

• Helps the fetus's muscles and bones develop

• Prevents the umbilical cord from compressing

Toward the end of pregnancy, the amniotic sac may rupture (this happens in less than 10% of pregnancies), often referred to as "water breaking or pre-labour rupture of membranes. Most commonly, this happens during labor, right before pushing, or in very rare circumstances the membranes stay intact and baby is born in the amniotic sac (known as "en caul). 

Sometimes a care provider may break the bag of water during labor, aka "artificial rupture of membranes" (AROM) or ‘Amniotomy’.

What are the contraindications of AROM?

• Fetal malpresentation or unstable lie 

• Vasa previa or velamentous cord insertion 

• Unengaged presenting part

• HIV infection

• Not in active labour

What are the benefits?

• Drug free

• Simple to perform and usually not painful

• May decrease the chances that you will need pitocin later on (in a spontaneous labour for someone who has given birth before)

• In combination with pitocin, AROM can help increase chances of a vaginal birth within 24 hours 

• Considered to be one of the safer induction/augmentation methods for VBAC

What are the considerations?

• If performed too early in the labor process, there can be an increased risk of infection

• Does not shorten labour for spontaneous, first time labours

• Increased risk of cord prolapse (approx 0.2% of births)

• In rare situations when not done properly, it may cause fetal scalp trauma

• Increases chance of cesarean

Is AROM alone an effective method for induction?

There is limited evidence to support using AROM alone as a method of labor induction, particularly for first-time births. Research found that when the cervix is favorable (slightly dilated and thinned), the most effective approach for achieving a vaginal birth within 24 hours is the combination of Pitocin and AROM (breaking the waters) 

AROM by itself did not shorten the first stage of labour. It DID decrease the use of pitocin augmentation, but only in those who had given birth before. 

What can I expect with AROM?

If you and your provider decide that an amniotomy is the best option for you and your baby, your provider will request that you get in a lithotomy position (on your back, similar to getting a cervical exam) 

They will then use what is called an “amniohook” to puncture a small hole in the amniotic sac. You shouldn’t feel any pain, but you may feel a gush of fluid or it may just be a trickle. 

Normally once the ‘cushion’ of fluids is released, it allows baby’s head to put more pressure on the cervix, causing contractions to intensify. 

Deciding what's best...

Because of the mixed evidence, amniotomy is not recommended as a routine practice for all labours. However, there are certain situations where AROM can be beneficial, and it’s important to have an informed discussion with your care provider so you can decide what is best for you.