When a person is in labor, a medical procedure known as an amniotomy, or artificial rupture of membranes (AROM), may be performed to help labor progress. This involves a healthcare provider intentionally breaking the amniotic sac, a fluid-filled membrane that surrounds and protects the developing baby throughout pregnancy. The amniotic sac contains amniotic fluid, which cushions the fetus from external pressures, regulates its temperature, and supports the development of its muscles, bones, lungs, and digestive system. While the amniotic sac typically ruptures naturally during labor, an amniotomy can be an option if it remains intact.
Reasons for Membrane Rupture
A healthcare provider may recommend an amniotomy for several reasons. One common indication is to induce labor, particularly when labor has stalled or is overdue. The rupture of membranes can release hormones, such as prostaglandins, which may stimulate uterine contractions and help the baby move deeper into the pelvis, thereby encouraging cervical dilation.
Another reason is to speed up slowly progressing labor by intensifying contractions. Additionally, an amniotomy allows for internal fetal monitoring, where a scalp electrode can be placed directly on the baby’s head to provide a more precise reading of the fetal heart rate than external monitoring.
This closer monitoring can be particularly useful if there are concerns about the baby’s well-being or if the mother is undergoing induction.
The Amniotomy Procedure
The amniotomy procedure is performed by a healthcare provider, typically an obstetrician or midwife, in a labor and delivery setting. The patient is usually positioned on their back with their knees bent and thighs apart, similar to a cervical examination. Before the procedure, the provider assesses cervical dilation and effacement, confirming the baby’s head is low and engaged. This minimizes complication risks.
To perform the amniotomy, a thin, sterile plastic tool called an amniohook or amnicot is commonly used. This instrument, often described as resembling a crochet hook with a small, rounded tip, is designed to puncture the amniotic sac. The provider carefully inserts the amniohook through the vagina and cervix, guiding it with their fingers to reach the amniotic sac. Once the sac is located, the provider uses the hook to make a small scratch or tear in the membranes, allowing the amniotic fluid to escape.
The procedure itself is generally not painful because the amniotic membranes do not have nerve endings. However, some individuals may feel a sensation of pressure or brief discomfort during the vaginal examination required to access the cervix and membranes. After the rupture, a warm sensation may be felt as the fluid is released.
What Happens During and After
Immediately following the amniotomy, individuals typically experience a release of amniotic fluid, which can manifest as either a sudden gush or a more gradual trickle. The amount of fluid released can vary depending on where the sac is punctured; a rupture below the baby’s head may result in a gush, while a higher tear might lead to a trickle. This fluid is usually clear or pale yellow and may be odorless, though it can sometimes be slightly blood-tinged.
The medical team closely monitors both the mother and baby after the procedure. The color and odor of the amniotic fluid are assessed, as greenish or foul-smelling fluid can indicate concerns such as the presence of meconium (fetal stool) or infection. Fetal heart rate monitoring is performed immediately and continuously to observe the baby’s response to the membrane rupture. Contractions often intensify or begin shortly after amniotomy, as the baby’s head presses more directly on the cervix.
Understanding Potential Risks
Amniotomy carries potential risks. One concern is the increased possibility of infection, particularly if there is a prolonged period between the rupture of membranes and the birth of the baby. The amniotic sac normally acts as a barrier against bacteria, and its rupture creates an open pathway, potentially leading to infections like chorioamnionitis.
Another important risk is umbilical cord prolapse, which occurs when the umbilical cord slips down into the vagina before the baby. This can compress the cord, reducing oxygen supply to the baby and potentially requiring an emergency cesarean section. The risk of cord prolapse is higher if the baby’s head is not well-engaged in the pelvis when the membranes are ruptured. Studies suggest that cord prolapse occurs in approximately 0.13% of amniotomies.
Amniotomy can also lead to changes in the fetal heart rate, specifically variable decelerations, due to increased pressure on the umbilical cord. While the procedure itself is not painful for the mother, the intensified contractions that often follow can lead to increased pain during labor.
Minor fetal scalp trauma is also a possibility if the baby’s head is very close to the membranes during the procedure.