Amniotomy

Anatomy and Physiology

The amniotic cavity is an enclosed space within the uterus in which the fetus develops and is protected during the antepartum period. The amniotic cavity is comprised of a dual-layer membrane, which includes an inner layer known as the amnion and an outer layer known as the chorion. This potential space forms early in pregnancy and is filled with serous fluid during the first few weeks of pregnancy. With further development of the fetus, specifically the fetal urinary system, the fluid in this potential space increases as the developing fetus excretes urine. Fetal urine comprises most of the amniotic fluid. Typically, this barrier remains intact throughout the duration of gestation, and the amniotic membranes will spontaneously rupture, releasing the amniotic fluid either immediately preceding spontaneous labor or sometimes after the onset of spontaneous labor.[1][2][3]

Indications

The two principal reasons for the artificial rupture of membranes are to induce or augment the labor process or to assist in the placement of internal fetal monitoring devices to provide a direct assessment of fetal status. Monitoring of the fetal heart rate as well as uterine activity can be easily obtained via external monitoring systems. However, in certain circumstances, a more direct evaluation of the fetal heart rate or uterine activity is required during labor. The amniotic membrane presents a physical impediment to this form of monitoring, and to place a fetal scalp electrode or intrauterine pressure catheter, the membranes must necessarily be broken before placement.[4][5]

Contraindications

Contraindications to this procedure are few and obvious. Artificial rupture of membranes should not be undertaken in the case of malpresentation, vasa previa, suspected velamentous insertion of the umbilical cord, or in the case of the unengaged fetal head or unstable lie. If the fetal presentation is unknown or not fully engaged, the risk for cord prolapse is increased. Additional contraindications include if the pregnant woman is not in active labor or if the patient refuses the intervention.

Equipment

• Amniotomy hook or amniotomy finger cot
• Sterile gloves and lubricant
• Personal protective equipment (gloves, gown, drapes, mask, eye protection)
• Absorbent pads and towels are to be placed under the patient
• Electronic fetal monitor (cardiotocography/CTG)
• Tocolytics should be available

Personnel

• Obstetrician or family medicine physician who provides obstetric care
• Midwife
• Labor and delivery nurse

Preparation

Amniotomy is easily performed with the use of specially designed hooks intended to grab and tear the amniotic membrane. The two most commonly used devices are an approximately 10-inch rod with a hook on the end of the rod or a finger cot with a hook on the end of the cot. With either device, the practitioner first assesses cervical dilation through the performance of a sterile digital exam. At the same time, assessment of the fetal presenting part is made, ensuring that the presenting part is, in fact, the fetal head and assessing that the fetal head is well engaged in the pelvis. After confirmation of both the fetal presentation and engagement, the practitioner can proceed with the artificial rupture of membranes.[6][7]

Technique or Treatment

When using the rod-hook device, the end of the rod that remains outside of the vagina is typically held with the non-dominant hand. The hook end of the rod is then protected between two fingers when entering the vagina. When the practitioner can palpate the amniotic membrane and the presenting part, the non-dominant hand advances the hook to the amniotic membrane. The membrane is then snagged with the hook, and gentle traction is applied in a superior direction to tear the amniotic membrane. Successful rupture of membranes is most commonly determined by the immediate return of amniotic fluid from the vagina. This fluid usually is clear and odorless. However, in certain circumstances, the fluid may contain meconium or be blood-tinged. It is important to note the color of the fluid at the time of rupture. Typically, following artificial rupture of membranes, the practitioner should not immediately remove their hand from the vagina because it is at this point that the highest risk of potential cord prolapse can occur and will be noted as the amniotic fluid continues to drain. After the immediate flow of amniotic fluid ceases, and there is no palpable cord in the vagina, the vaginal hand can then be removed.

Complications

Complications also are relatively few. The rupture of membranes does eliminate the primary barrier between the fetus and the polymicrobial environment of the vagina. If performed too early in the labor process, there can be an increased risk of intrapartum chorioamnionitis. The most common complication of artificial rupture of membranes is prolapse of the umbilical cord. This invariably occurs after rupture if artificial rupture of membranes is performed when the head is not engaged in the maternal pelvis. In the case of an unengaged fetal head, the rupture of membranes may allow for the umbilical cord to precede the fetal head when the release of amniotic fluid occurs. This will allow the fetal head to compress the section of the umbilical cord preceding the head, generally leading to fetal bradycardia and necessitating emergency cesarean section. This complication should be an easily avoidable, iatrogenic cause of emergency delivery.[8]

Clinical Significance

Practitioners have believed that artificial rupture of membranes can either assist in inducing labor or augmenting spontaneous labor. It is commonly felt that relieving the amniotic sac of amniotic fluid induces uterine contraction activity, increases the strength of contractions, and may augment labor by allowing direct pressure from the fetal scalp on the uterine cervix which may assist in dilating the cervix. While these are commonly held beliefs of many practitioners, the data to support amniotomy for these reasons is uncertain. Some studies have produced data supporting the practice, while others suggest that this practice does not accomplish any of these outcomes. As a result, meta-analysis has been performed; however, the data has been mixed. Meta-analysis suggests that amniotomy to shorten spontaneous labor does not produce a discernible difference compared to no amniotomy. Nevertheless, when there is a delay in labor, the meta-analysis suggests a modest reduction in the rate of cesarean section when the rupture of membranes in conjunction with oxytocin is used as an early intervention.

Enhancing Healthcare Team Outcomes

Amniotomy, also known as artificial rupture of membranes (AROM), is best performed by an obstetric clinician or a midwife in the labor and delivery department. Prior to the procedure, the nurse needs to assist the provider by preparing the necessary equipment, monitoring the vital signs of the patient, and reporting any untoward changes to the care provider. The nurse plays a vital role during the procedure in monitoring the mother as well as the fetus; they also note the color of the draining amniotic fluid and document the findings in the medical chart. After the procedure, they assess the maternal temperature every two hours and watch for any signs of infection. The nurse also monitors the fetal heart rate via continuous electronic fetal monitoring and communicates the findings to the provider. The nurse needs to frequently change underpads. One of the most crucial roles of the nurse is to educate the woman about the amniotomy procedure and address the patient's concerns at all times. Only through interprofessional collaboration and integration can the best standard of care for both the mother and the fetus be achieved.

Nursing, Allied Health, and Interprofessional Team Interventions

The nurse has an important role in the assessment and continuous monitoring of pregnant women in labor. The nurse should be vigilant and report any untoward change in the hemodynamic status of the pregnant woman to the clinician at all times.

Nursing, Allied Health, and Interprofessional Team Monitoring

• Hemodynamic status of the pregnant woman
• Vital signs
• Any signs of infection
• Any signs of cord prolapse
• Fetal heart rate
• Color of the amniotic fluid (liquor)