Amniotomy or the artificial rupture of membranes (AROM) is a procedure in which the bag of water around the fetus (amniotic sac) is ruptured by a healthcare professional to start the labor pains. Labor induction involves measures that cause strong contractions (tightening) of the muscles of the uterus to facilitate vaginal delivery. The procedure is typically done at the patient’s bedside in the labor or delivery suite.
Amniotomy involves making a small hole in the amniotic sac. This starts contractions of the uterus or strengthens the contractions if they have already begun. The contractions occur due to several mechanisms, such as an increase in certain chemicals, called prostaglandins in the body.
The doctor begins by examining whether the cervix is thin and dilated (opened up) and the head of the baby has moved down into the pelvis (engaged). Amniotomy is done by using a specialized instrument called an amniotic perforator or amniotic hook. The doctor guides the hook through the cervix, using their fingers to prevent any injury. The procedure is not associated with any significant discomfort or pain. The bulge of the amniotic sac is felt, and a small hole is made by the instrument. This is followed by a gush of amniotic fluid (the water). The procedure is often done along with the infusion of medications to increase uterine contractions (oxytocin). The doctor examines the color, odor, and quantity of the fluid. Labor often starts within hours of amniotomy.
Why is amniotomy done?
Amniotomy is done to:
- Induce the contractions of the uterus for facilitating vaginal delivery
- Assist in internal fetal monitoring to know the well-being of the fetus
- Augment or speed-up the process of labor
The procedure is done when the cervix (neck of the uterus) is thin and dilated and the head of the baby has moved down into the pelvis (engaged).
Amniotomy should not be done if there is:
- Known or suspected abnormality called vasa previa (a condition in which blood vessels within the placenta or the umbilical cord are trapped between the fetus and the opening to the birth canal)
- Presence of any contraindications to vaginal delivery, such as placental abruption (a condition in which the placenta separates too soon from the wall of the uterus), persistent fetal distress, cephalopelvic disproportion (the baby's head or body is very large to fit through the birth canal)
- Unengaged head or other presenting part of the fetus (this may be overcome by using a controlled amniotomy or the application of fundal or suprapubic pressure)
What are the complications of an amniotomy?
Amniotomy is often a safe and painless procedure. There may be some complications of this procedure, such as:
- Cord prolapse: It is the most common complication of amniotomy. Cord prolapse is a condition in which the umbilical cord enters the birth canal before the baby. It usually occurs when there is a sudden and rapid outflow of the amniotic fluid.
- Infections: Opening the bag of water may increase the risk of infections, such as chorioamnionitis (acute inflammation of the fetal membranes and the placenta).
- Cord compression: The compression or pinching of the umbilical cord may affect the baby’s oxygen supply.
- Injuries: There may be a risk of injury to the mother or the baby. Minor injury to the fetal scalp may occur if the head was close to the membranes when the amniotomy was done.
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