Cord Occlusion

What is Cord Occlusion?

Refers to a procedure where the umbilical cord circulation is stops to interrupt blood supply to an abnormal identical twin (monochorionic pregnancy). In fraternal twins (dichorionic) where selective feticide is performed or indicated, Potassium chloride is typically the agent used. Due to concern to communicating vessels across the placenta in identical twin pregnancies, this procedure is not performed, and other cord occlusive methods must be applied.

Currently, there are many different procedures described in the literature such as:

  • Bipolar cord ligation:This procedure is done inside the uterus, through a sheath or large bore needle placed by ultrasound guidance in the sac of one twin, usually the donor (smaller) twin. Special bipolar tweezers grasp the cord and an electric current passes between the jaws of the tweezers, coagulating the blood vessels of that twin’s cord. This stops the flow of blood in the cord and that fetus will die.
  • Laser cord occlusion: A laser fiber is used either through a scope inside the uterus or a large bore needle. Under direct US guidance, the laser fibre is threaded through the needle or through the scope. A power output between 20-100 watts is required to achieve complete occlusion, depending on gestation and cord size. In this group, an amnioreduction is usually performed.
  • Unipolar cord ligation:This procedure is done inside the uterus, through a large bore needle placed by ultrasound guidance in the sac of one of the affected twins. A wire electrode is wrapped around the cord, and an electric current passes coagulating the blood vessels of that twin’s cord. This stops the flow of blood in the cord and that fetus will die.
  • Cord ligation: Under continuous ultrasound (US) guidance, a cannula is introduced into the amniotic cavity, and a large needle passed through it. Blood can be sampled from the “pump” twin’s placental cord root and a medication can be used to paralyze both twins. An operating trocar is then placed into the amniotic sac approximately 10 cm from the previous needle site. Using both access points, a suture is placed around the acardiac (parasitic twin) twin’s cord under US guidance and tied, resulting in interruption of blood flow in the cord. An amnioreduction is sometimes performed.
  • Radiofrequency ablation 

For what conditions is Cord Occlusion performed?

Cord occlusion is considered an option in identical twin pregnancies (Monochorionic) where there are complications:

  • Severe Twin-to-twin transfusion where there is concern for death of one twin or severe brain damage.
  • Severe cases of growth discordances with abnormal Dopplers or brain anomalies.
  • Severe discordant anomaly both for parental decision or impending damage to normal fetus.
  • Acardiac fetus or TRAP Sequence with polyhydramnios or cardiac overload (1% monozygotic twins).   An acardiac twin is a parasitic twin, who fails to develop a normal heart, and relies on an abnormal circuit with a normal twin to survive. This twin is not able to survive without this circuit, and there is concern for the normal twin’s survival due to cardiac failure.

What are the risks of Cord Occlusion to fetus?

As with any intrauterine invasive procedure, there may be short term complications, including preterm labor, rupture of membranes, infection or bleeding. This means that not all such procedures result in one living baby. But, in about 60-85% of cases (depending on procedure), the procedure results in one living baby, born near term, with no permanent handicaps. The optimal technique has not yet been established, although a few reports report good survival and less complications with RFA.

Because the umbilical cord is completely blocked, this procedure means survival of both babies can never occur.

What are the risks of Cord Occlusion to mother?

For an experienced team, this procedure is technically feasible and usually not long, so maternal operative complications are very unusual. There may be risks related to anesthetic use.

References:

Roman, a, Papanna, R., Johnson, a, Hassan, S. S., Moldenhauer, J., Molina, S., & Moise, K. J. (2010). Selective reduction in complicated monochorionic pregnancies: radiofrequency ablation vs. bipolar cord coagulation. Ultrasound in Obstetrics & Gynecology : The Official Journal of the International Society of Ultrasound in Obstetrics and Gynecology, 36(1), 37–41. doi:10.1002/uog.7567

Bebbington, M. W., Danzer, E., Moldenhauer, J., Khalek, N., & Johnson, M. P. (2012). Radiofrequency ablation vs bipolar umbilical cord coagulation in the management of complicated monochorionic pregnancies. Ultrasound in Obstetrics & Gynecology : The Official Journal of the International Society of Ultrasound in Obstetrics and Gynecology, 40(3), 319–24. doi:10.1002/uog.11122

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