01
Physiological Functions of the Amniotic Membrane
At term, the amniotic membrane is a tough and flexible membrane. This innermost avascular fetal membrane secretes and absorbs amniotic fluid, playing an extremely important role in human pregnancy. The amniotic membrane provides almost all of the tensile strength of the fetal membranes, and the amniotic epithelium can synthesize vasoactive peptides and prostaglandins, which enter the surface of the chorion to promote cervical maturation and uterine contractions.
02
Clinical Applications of Artificial Rupture of Membranes (ARM)
1. Inducing Contractions — Induction of Labor
When the cervical conditions are immature, with a Bishop score ≤6, simple ARM not only has a low success rate for induction but also cannot predict the timing of labor onset. Additionally, the long duration from membrane rupture to delivery may lead to infection; therefore, it is not recommended to use ARM alone to promote cervical maturation. ARM is often combined with medication or mechanical methods to induce cervical maturation. When the cervical conditions are mature, with a Bishop score ≥7, ARM can be combined with oxytocin for induction.
Indications for ARM Induction:
(1) Conditions for vaginal trial of labor induction (IOL) are met.
(2) Bishop score ≥7.
Relative Contraindications:
(1) Fetal head not engaged in the pelvis.
(2) Fetal head not in close contact with the cervix.
ARM is more commonly used after inducing regular contractions with medication or mechanical methods. For example, if the Bishop score ≤6, a balloon catheter is placed for induction, and after 12 hours, the balloon is removed. It is recommended to immediately start intravenous oxytocin after ARM; if cervical maturation with the balloon is ineffective or not significant, and ARM cannot be performed, sequential use of dinoprostone for cervical maturation or re-insertion of the cervical balloon after 24 hours may be considered. Currently, some scholars in China believe that after ARM, observation for 30-60 minutes is necessary; if there are no intensified contractions, a small dose of oxytocin can be used again.
2. Shortening Labor Duration — Augmentation of Labor
Routine ARM during labor is not recommended: The 2020 Clinical Practice Guidelines for Normal Labor established by the Obstetrics Group of the Chinese Medical Association and the Perinatal Medicine Group clearly state that routine ARM during labor is not recommended.
ARM is not recommended during the latent phase, but is recommended during the active phase: At term, the chorion in direct contact with the cervical opening reduces the release of prostaglandin-degrading enzyme (PDHG), allowing prostaglandins in the amniotic membrane to contact the cervix, promoting cervical maturation and shortening labor duration.
If ARM is performed early, the effects of these prostaglandins on the cervix will disappear, and the intrauterine environment will be prematurely exposed to the outside, increasing the risk of chorioamnionitis. Therefore, ARM during the latent phase is not recommended.
Once in the active phase, ARM generally refers to rupture of membranes when the cervical dilation is ≥5cm. If there is a lack of coordinated contractions after ARM, oxytocin can be used to promote labor progression. The combination of ARM and intravenous oxytocin can shorten the time from induction to delivery. If the membranes remain intact after full cervical dilation, affecting fetal descent, ARM can be performed during contraction intervals to facilitate fetal descent and manual rotation of the fetal head.
3. Adjusting Fetal Position (ARM + Manual Rotation of Fetal Head)
For pregnant women with abnormal fetal positions, entering the second stage of labor or nearing complete cervical dilation, when the biparietal diameter of the fetal head reaches the plane of the ischial spines or lower, manual rotation of the fetal position after ARM is the primary measure for correcting fetal position.
4. ARM for Vaginal Delivery of Twins
ARM is not recommended during the first stage of labor. In our clinical practice, an interval of 5-10 minutes between the deliveries of two fetuses is preferable.
After the first fetus is delivered, quickly stabilize the second fetus in a longitudinal position. If the first fetus is in a breech position, it can be grasped by the ankle through the relaxed cervical opening across the amniotic sac and pulled to the vaginal opening. During contraction intervals, ARM can be performed, followed by breech assistance or breech extraction; if the second fetus is in a vertex position, an assistant can gently push down the fundus of the uterus, and after the fetal head engages in the pelvis, ARM can be performed during contraction intervals to deliver the fetus.
After the first fetus is delivered, administer oxytocin intravenously as needed based on contraction status.
03
Precautions for ARM Operation
and Emergency Management of Cord Prolapse
The timing for membrane rupture should be selected between two contractions, adhering to the “three protections”: prevent rapid outflow of amniotic fluid leading to cord prolapse; prevent sudden drop in intrauterine pressure leading to placental abruption; do not perform artificial membrane stripping simultaneously to avoid amniotic fluid entering the bloodstream during contractions, which could lead to amniotic fluid embolism. A significant complication of ARM is cord prolapse.
Risk factors include: performing ARM when the fetal presentation is not engaged, rupturing membranes during external rotation of a breech presentation, amniotic fluid infusion, placement of fetal scalp electrodes or intrauterine pressure catheters, or using balloon catheters for cervical maturation.
Most cases of cord prolapse occur within minutes after membrane rupture. One study found that 57% occurred within 5 minutes, and 67% occurred within 1 hour after rupture. If fetal heart rate deceleration or variability occurs within minutes after ARM, especially if abnormal fetal heart monitoring occurs immediately after membrane rupture, one should be alert for possible cord prolapse. If cord prolapse is diagnosed, vaginal delivery is not possible in the short term, and immediate cesarean section should be performed. If blood-stained amniotic fluid is present after ARM, with or without fetal heart rate abnormality, there is a high suspicion of placental abruption.
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Source: Department of Obstetrics and Gynecology, Xi’an Jiaotong University First Affiliated Hospital
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