Amniotomy 

Updated: Aug 09, 2016
Author: Nan G O'Connell, MD; Chief Editor: Christine Isaacs, MD 

Overview

Background

Amniotomy (also referred to as artificial rupture of membranes [AROM]) is the procedure by which the amniotic sac is deliberately ruptured so as to cause the release of amniotic fluid. Amniotomy is usually performed for the purpose of inducing or expediting labor or in anticipation of the placement of internal monitors (uterine pressure catheters or fetal scalp electrodes). It is typically done at the bedside in the labor and delivery suite.

Indications and Contraindications

Amniotomy is indicated in the following situations:

  • When internal fetal or uterine monitoring is needed[1]

  • For induction of labor, usually in conjunction with an oxytocin infusion[2, 3, 4, 5, 6, 7]

  • For augmentation of labor, in that amniotomy leads to an increase in plasma prostaglandins[8] ; data on the effectiveness of labor augmentation are mixed[9, 10]

Amniotomy may be contraindicated in the following situations:

  • Known or suspected vasa previa

  • Any contraindications to vaginal delivery

  • Unengaged presenting part (although this obstacle may be overcome with the use of a controlled amniotomy or the application of fundal or suprapubic pressure)

 

Periprocedural Care

Equipment

Equipment for amniotomy includes the following:

  • Examination gloves

  • Vaginal speculum and spinal needle (if a controlled amniotomy is to be performed)

  • Amniotic membrane perforator: This may be an amniotomy hook, such as the AmniHook (Briggs Healthcare, West Des Moines, IA), or an amniotomy finger cot, such as the Amnicot (Allied Medical, Perth, Australia) or the AROM-Cot (Utah Medical Products, Midvale, UT).*

The AmniHook is a rigid, plastic device with a pointed tip at the end of smooth curve, attached to a 10-in. handle (see the first image below). The Amnicot has a pointed plastic tip embedded in a latex or latex-free finger cot (see the second image below); the AROM-Cot is similar.

Amniotomy hook. Amniotomy hook.
Amnicot Amnicot

Patient Preparation

Amniotomy is usually performed with the patient supine in the labor bed, with knees and hips flexed (ie, “frog-legged”). It may also be performed with the patient in the lithotomy position, especially if a speculum is required.

Once the patient is positioned, sterile gloves are donned. The dominant hand is used to perform a cervical examination to assess dilation, effacement, position, and station. The presenting fetal part should be determined to be well applied to the cervix before performing amniotomy.

 

Technique

Artificial Rupture of Amniotic Sac

Once amniotomy can be safely performed, the amniotic membrane perforator is advanced. If an amniotic hook is used, the handle of the device is held with one hand outside the vagina while 2 fingers of the opposite hand are placed in the vagina to guide the tip. Care should be taken to protect maternal tissues from the point. If an amniotic finger cot is used, the device is placed on the index or middle finger of the examining hand.

Once the hook reaches the amniotic sac, the tip is pushed up against the sac with the index or middle finger of the internal hand to pierce the membranes. The hook is then pulled through the membranes with the external hand holding the handle to create a hole in the sac. If an amniotic finger cot is being used, the pointed tip is dragged through the membranes with the finger to create the amniotomy.

The examining hand should remain in place to confirm that there has been no prolapse of the umbilical cord during the amniotomy.

The hand is then removed from the vagina The nature of the amniotic fluid (ie, clear, bloody, meconium-stained, or purulent) is documented, and the fetal heart rate should be monitored for several minutes after the procedure.

Approach to unengaged presenting part

If amniotomy is required but the presenting part is not well engaged, an assistant can apply external fundal or suprapubic pressure to keep the fetus in place while the amniotic fluid is slowly released. Before amniotomy, this pressure should be determined to be adequate to ensure that the fetal head is applied to the cervix.

When this technique is not feasible or has been attempted without success, a controlled amniotomy can be performed. In this instance, the patient should be taken to the cesarean suite and placed in the lithotomy position. A speculum is placed in the vagina, and the amniotic sac is visualized. A spinal needle is then used to make 1 or more small holes in the sac, thereby very slowly releasing amniotic fluid under direct visualization and allowing the presenting part to descend safely into the pelvis.

Complications

The most common complication of amniotomy is cord prolapse, which usually occurs during the sudden and rapid egress of amniotic fluid. Rupture of a vasa previa during amniotomy can cause life-threatening fetal blood loss. Both of these complications require emergency cesarean delivery.

An increased incidence of chorioamnionitis is seen, especially with prolonged rupture of membranes. Cord compression associated with variable decelerations of the fetal heart rate occurs more often after amniotomy. Minor fetal scalp trauma may also occur, especially if the fetal head is closely applied to the membranes when amniotomy is performed.