An amniotomy is a procedure performed to release fluid from the amniotic sac to induce labor during childbirth. It is also performed when certain pregnancy-related conditions require the placement of internal monitors such as fetal scalp electrodes and uterine pressure catheters. The procedure is usually performed in a labor or delivery room wherein the obstetrician punctures the amniotic membrane using special surgical tools.
Pregnant women should are advised to under an amniotomy in the following conditions:
If labor needs to be augmented, with the procedure helping increase the patient’s plasma prostaglandins
There are many reasons when labor induction may be deemed necessary, such as when:
Fetal distress is detected
However, there are conditions wherein an amniotomy or other methods of labor induction is not advised, such as:
After an amniotomy, the patient is expected to give birth within 24 hours. If not, there is an increased risk of intrauterine infection, and this may pose severe harm to the fetus even when antibiotics are administered. If birth does not occur within the allotted time, the doctor will recommend either a controlled amniotomy or a caesarean section.
An amniotomy is performed by an obstetrician in a labor or delivery room, with the patient lying on a hospital bed. In some cases, the patient is asked to stay in a semi-sitting position to minimize cord compression and ensure good oxygen supply for the fetus.
The procedure is done using either an amniotic membrane perforator, also known as an amniotomy hook or AmniHook, or an amniotic finger cot, known by the brand names Amnicot and AROM-Cot. The obstetrician will also use a vaginal speculum, or a spinal needle if the patient’s condition or other circumstances require a controlled amniotomy.
Before performing the procedure, certain steps have to be performed to prepare the patient. First, it is crucial to determine the fetus’ presentation and location. Second, the pregnant patient may need to be placed on electronic fetal monitor.
It is also important that the fetal head applies a sufficient amount of pressure on the cervix for the procedure to be effective. If conditions demand an amniotomy but the presenting fetal part is not yet engaged properly, the doctor’s assistant may apply external pressure on the fundal or suprapubic to hold the fetus in the right presenting position as the amniotomy is performed.
When the patient has been prepped for the procedure, the obstetrician proceeds to dilate the cervix in a process similar to that used when performing an internal cervical examination. The doctor then ruptures the amniotic membrane using the hook, timing it in between contractions. As the amniotic fluid begins to flow out, the doctor keeps one hand in the vagina to let it flow in a gradual manner and prevent umbilical cord prolapse. As a follow-up step, the doctor measures and notes the color and consistency of the fluid that comes out.
After an amniotomy, the fetus’ heartbeat will be assessed for one full minute, which is also performed prior to the procedure. This is to check for any changes in the fetus’ condition and any warning signs that may signal fetal distress.
There are certain complications associated with an amniotomy. These include:
Chorioamnionitis – This is associated with prolonged membrane rupture.
Cunningham, Levano, Bloom, Hauth, Rouse, Spong. Abnormalities of the Placenta, Umbilical Cord and Membranes. Williams Obstetrics. 23rd. United States: McGraw-Hill; 2010. Chapter 27.
Nachum Z, Garmi G, Kadan Y, Zafran N, Shalev E, Salim R. Comparison between amniotomy, oxytocin or both for augmentation of labor in prolonged latent phase: a randomized controlled trial. Reprod Biol Endocrinol. 2010. 8:136.