Twin pregnancies require careful monitoring because they may be associated with specific complications that can affect fetal health and pregnancy outcomes. Among these rare and complex complications is Twin Reversed Arterial Perfusion (TRAP) Sequence, a condition that occurs primarily in monochorionic twin pregnancies due to abnormal vascular connections within the placenta. These connections lead to a severe disruption of blood circulation between the two fetuses.TRAP sequence is characterized by the presence of a relatively normally developed twin, known as the pump twin, which pumps blood to a severely malformed twin, known as the acardiac twin. This occurs through an abnormal arterial blood flow that travels in the opposite direction to normal circulation. This unusual pattern of perfusion prevents the acardiac twin from developing normally while placing an additional burden on the cardiovascular system of the pump twin. As a result, serious complications may arise, including cardiac failure, fetal hydrops, and preterm birth.The significance of this condition lies not only in the severe malformations affecting the acardiac twin but, more importantly, in the risks posed to the pump twin, whose survival depends on maintaining adequate blood circulation and normal cardiac function. Therefore, early diagnosis and close monitoring using ultrasonography and Doppler studies are essential for assessing the severity of the condition, evaluating potential risks, and determining the most appropriate intervention.At Medica Guide, understanding TRAP sequence is essential to recognizing its pathophysiology, types, diagnostic features, and potential complications, as well as exploring the latest available treatment options. These interventions aim to interrupt the reversed blood flow, protect the pump twin, and improve pregnancy outcomes.

1. What Is Twin Reversed Arterial Perfusion (TRAP) Sequence?

   Twin Reversed Arterial Perfusion (TRAP) sequence is a rare complication of monochorionic twin pregnancies in which one twin, known as the pump twin, is relatively normally developed, while the other, known as the acardiac twin, is severely malformed and lacks a functional heart. The condition is characterized by reversed arterial blood flow from the pump twin to the acardiac twin through abnormal vascular connections within the shared placenta.

   Why Does TRAP Sequence Occur?

   TRAP sequence develops as a result of abnormal vascular connections between the two twins within the shared placenta. These connections allow blood to flow from the pump twin to the acardiac twin in the opposite direction to normal blood circulation.

   This abnormal perfusion prevents the acardiac twin from developing normally, while placing an additional workload on the cardiovascular system of the pump twin.

   Does the Mother Experience Any Symptoms?

   In most cases, the mother does not experience any clear or specific symptoms during the early stages of pregnancy. The condition may be discovered incidentally during a routine ultrasound examination.

   In some cases, symptoms related to complications may develop later, including:

   • Increased amniotic fluid volume (polyhydramnios).

   • Excessive uterine enlargement.

   • Discomfort or shortness of breath.

   • An increased risk of preterm birth.

   How Is TRAP Sequence Diagnosed?

   Diagnosis primarily relies on ultrasonography with Doppler assessment, which helps evaluate both twins and determine the direction of blood flow between them.

   The main diagnostic features include:

   • Presence of a severely malformed twin: Identification of the acardiac twin.

   • Absence of a functional heart: The acardiac twin lacks a functioning heart or detectable cardiac activity.

   • Reversed arterial blood flow: Doppler examination demonstrates abnormal arterial perfusion within the acardiac twin, which is the hallmark of TRAP sequence.

   • Assessment of the pump twin's size and growth: Evaluation of fetal growth and development.

   • Evaluation of cardiac function: Assessment of the pump twin's heart for signs of cardiovascular strain or heart failure.

   • Assessment of fetal and placental blood flow: Doppler studies help evaluate the severity of the condition.

   What Is the Most Important Diagnostic Finding on Doppler Ultrasound?

   Reversed arterial flow within the acardiac twin is one of the most important diagnostic features of TRAP sequence.

   Doppler ultrasound demonstrates blood entering the acardiac twin through the umbilical artery in a direction opposite to normal fetal circulation. This abnormal flow pattern distinguishes TRAP sequence from other complications of twin pregnancies.

   Can the Acardiac Twin Survive?

   The acardiac twin cannot survive independently because it lacks a functional heart and has severe structural abnormalities.

   Therefore, the primary goal of treatment is to protect the pump twin from complications caused by the additional circulatory workload and to improve the chances of a favorable pregnancy outcome.

   What Is the Most Serious Complication Affecting the Pump Twin?

   One of the most serious complications is high-output cardiac failure, which occurs when the pump twin's heart must circulate additional blood to support perfusion of the acardiac twin. This places excessive strain on the pump twin's heart and cardiovascular system.

   In advanced cases, the condition may progress through the following sequence:

   Cardiac failure → Hydrops fetalis → Intrauterine fetal death.

   What Factors Increase the Severity of TRAP Sequence?

   The risk to the pump twin increases when one or more of the following factors are present:

   • A large acardiac twin relative to the pump twin.

   • Increased blood flow to the acardiac twin.

   • Signs of cardiac strain or impaired cardiac function in the pump twin.

   • Development of fetal hydrops (hydrops fetalis).

   • Abnormal findings on Doppler ultrasound.

   • Increased amniotic fluid volume (polyhydramnios).

   These findings help clinicians assess the severity of the condition and determine whether intervention may be necessary.

   Can the Pump Twin Die?

   Yes. In severe cases, the persistent additional workload on the pump twin's cardiovascular system may lead to heart failure and, ultimately, intrauterine fetal death.

   However, early diagnosis, close monitoring with ultrasound and Doppler studies, and appropriate intervention when indicated aim to reduce complications, protect the pump twin, and improve the chances of pregnancy continuation.

   The management plan depends on factors such as gestational age, the size of the acardiac twin, blood-flow characteristics, and the pump twin's cardiac function. Specialized fetal medicine assessment is essential to determine the most appropriate approach.

2. What Is the Difference Between TRAP Sequence and the Death of One Twin?

   Twin Reversed Arterial Perfusion (TRAP) sequence differs from the death of one fetus in a twin pregnancy. In TRAP sequence, one twin, known as the acardiac twin, is severely malformed, and abnormal vascular connections between the twins cause reversed arterial blood flow. As a result, the acardiac twin receives blood from the pump twin.

   In contrast, the death of one twin does not necessarily indicate TRAP sequence. Fetal death may occur for various reasons without the presence of an acardiac twin or reversed arterial blood flow.

   Ultrasound with Doppler assessment is one of the most important diagnostic tools for distinguishing between these conditions because it identifies the blood-flow pattern and detects the reversed arterial perfusion characteristic of TRAP sequence.

   What Are the Types of Acardiac Twins in TRAP Sequence?

   Acardiac twins are classified according to the degree of anatomical development and the formation of their body structures. The main types include the following:

   1. Acardius Acephalus

   This is one of the most common types. It is characterized by the absence or severe underdevelopment of the head and brain, while the trunk and limbs may be present to varying degrees.

   Some thoracic or abdominal organs may be present, but the heart is absent or functionally undeveloped.

   2. Acardius Anceps

   This type is characterized by a partially developed head, although the head and brain remain severely malformed and incompletely developed.

   Some facial features may be present, making this type more anatomically developed than the acephalus type.

   3. Acardius Acormus

   This rare type is characterized by a relatively developed head with an absent or severely underdeveloped trunk. It is one of the less common forms of TRAP sequence.

   4. Acardius Amorphus

   In this type, the acardiac twin appears as a largely undifferentiated mass of tissue, making it difficult to identify normal body structures clearly.

   Distinct anatomical features of the head, trunk, or limbs are generally absent, and the heart is not present as a functional organ.

   What Causes Twin Reversed Arterial Perfusion (TRAP) Sequence?

   Twin Reversed Arterial Perfusion (TRAP) sequence is a rare complication of monochorionic twin pregnancies. It involves a relatively normally developed twin, known as the pump twin, and a severely malformed twin, known as the acardiac twin, which lacks a functional heart.

   How Does TRAP Sequence Develop?

   TRAP sequence is associated with abnormal vascular connections between the two twins within their shared placenta. These connections include artery-to-artery anastomoses, which allow blood from the pump twin's circulation to flow toward the acardiac twin.

   As a result:

   • Blood flows from the pump twin to the acardiac twin through the interconnected placental vessels and umbilical circulation.

   • Blood enters the acardiac twin in the opposite direction to normal fetal circulation, giving the condition its name.

   • The blood reaching the acardiac twin is relatively poorly oxygenated, contributing to abnormal development of its organs, particularly the heart, brain, and upper body structures.

   • The pump twin must maintain its own circulation while also supplying blood to the acardiac twin, increasing the workload on its cardiovascular system.

   As this additional workload continues, the pump twin may develop cardiac strain or high-output cardiac failure. In severe cases, this may progress to fetal hydrops or intrauterine fetal death.

   What Leads to the Development of an Acardiac Twin?

   The development of an acardiac twin is believed to be associated with an early disturbance in embryonic and placental circulation during the initial stages of fetal development, together with abnormal vascular connections between the twins.

   Abnormal blood flow and inadequate oxygen delivery disrupt the development of certain fetal structures, particularly the heart and upper body. This results in an acardiac twin with varying degrees of anatomical malformation.

   Therefore, TRAP sequence is not simply a condition in which the heart of a previously normal twin stops beating. Rather, it is associated with early abnormalities in embryonic development and fetal circulation.

   Why Is TRAP Sequence Associated With Monochorionic Twins?

   TRAP sequence occurs primarily in monochorionic twin pregnancies because both twins share a single placenta, allowing vascular connections to form between their circulatory systems.

   In dichorionic twin pregnancies, the twins generally have separate placentas, so the shared placental vascular connections responsible for the characteristic reversed arterial perfusion pattern are usually absent.

   What Are the Symptoms and Signs of TRAP Sequence?

   TRAP sequence usually does not cause clear or specific symptoms in the mother during early pregnancy. It is often detected during routine prenatal ultrasonography.

   The clinical findings vary according to the severity of the condition and the status of the pump twin.

   Symptoms and Signs That May Occur in the Mother

   Symptoms may develop, particularly when pregnancy complications arise. These may include:

   • Abdominal or uterine enlargement that is greater than expected for gestational age.

   • Increased amniotic fluid volume (polyhydramnios).

   • A sensation of abdominal fullness or pressure.

   • Shortness of breath due to excessive uterine enlargement and increased amniotic fluid.

   • Abdominal discomfort or pain.

   • Uterine contractions in some cases.

   • An increased risk of preterm birth.

   However, the absence of symptoms does not rule out TRAP sequence. The mother may remain completely asymptomatic, with the condition detected during routine ultrasound screening.

   Ultrasound Findings in the Acardiac Twin

   The acardiac twin may demonstrate the following findings on ultrasound:

   • Absence of a heart or functional cardiac structure.

   • Incomplete development of the head and brain to varying degrees.

   • Severe underdevelopment of the upper body.

   • Major malformations involving the trunk, limbs, and internal organs.

   • An abnormally formed fetal mass whose appearance varies according to the type of acardiac twin.

   • Reversed arterial blood flow within the acardiac twin on Doppler examination, one of the most characteristic findings of TRAP sequence.

   Signs Affecting the Pump Twin

   The pump twin may appear relatively normal during the early stages of pregnancy. However, persistent reversed perfusion can gradually increase the workload on its heart and cardiovascular system.

   Signs of cardiovascular strain may include:

   • Cardiomegaly (enlargement of the heart).

   • Impaired myocardial function.

   • Tricuspid regurgitation.

   • Abnormal blood-flow patterns in certain fetal vessels.

   • Signs of high-output cardiac failure.

   • Fetal hydrops in advanced cases.

   • Increased amniotic fluid volume.

   Repeated ultrasound examinations, Doppler studies, and assessments of cardiac function are essential for determining disease severity and monitoring progression.

   How Is Twin Reversed Arterial Perfusion (TRAP) Sequence Diagnosed?

   Diagnosis primarily relies on ultrasonography with Doppler assessment during pregnancy. The diagnosis does not depend on maternal symptoms because the mother is often asymptomatic, and the condition is frequently discovered during routine prenatal examinations.

   Key Diagnostic Findings

   1. Presence of a Monochorionic Twin Pregnancy

   TRAP sequence usually occurs in monochorionic twin pregnancies, in which both twins share one placenta. This shared placental circulation permits vascular connections to develop between their blood supplies.

   A shared placenta is an important finding that supports the diagnosis, but it is not sufficient on its own to confirm TRAP sequence.

   2. Identification of the Acardiac Twin

   Ultrasound may reveal a severely malformed fetus with the following features:

   • Absence of a heart or detectable cardiac activity.

   • Incomplete development of the head or brain to varying degrees.

   • Severe underdevelopment of the upper body.

   • Major abnormalities involving the trunk, limbs, and internal organs.

   • Variations in the size and appearance of the acardiac twin depending on its degree of anatomical development.

   3. Confirmation of Reversed Arterial Perfusion Using Doppler

   Doppler ultrasound is the key diagnostic technique for demonstrating the characteristic reversed arterial blood flow.

   In TRAP sequence, blood enters the acardiac twin through the umbilical artery in a direction opposite to normal fetal circulation.

   This finding is highly characteristic of TRAP sequence and helps distinguish it from other fetal malformations and cases of single-twin demise.

   4. Assessment of the Pump Twin

   Evaluation must extend beyond the acardiac twin to determine how the abnormal circulation affects the pump twin.

   The assessment includes:

   • Measuring the fetal heart rate.

   • Evaluating heart size and cardiac function.

   • Looking for signs of cardiac strain or failure.

   • Detecting fetal hydrops.

   • Assessing blood flow in the umbilical artery.

   • Evaluating blood flow in the ductus venosus.

   • Looking for other signs of increased cardiovascular workload.

   This evaluation is essential for determining the severity of the condition, assessing the risk to the pump twin, and deciding whether therapeutic intervention may be necessary.

   How Can TRAP Sequence Be Distinguished From the Death of One Twin?

   This distinction is important in the differential diagnosis.

   In TRAP sequence, the acardiac twin lacks normal cardiac activity, but Doppler ultrasound demonstrates reversed arterial blood flow within its body due to the continued circulation supplied by the pump twin.

   In contrast, when one twin dies in utero for other reasons, the characteristic reversed arterial perfusion pattern of TRAP sequence is not expected.

   Therefore, demonstrating reversed arterial blood flow with Doppler ultrasound is a key factor in distinguishing an acardiac twin in TRAP sequence from a fetus that has died in utero.

   Surgical Treatment of Twin Reversed Arterial Perfusion (TRAP) Sequence

   Surgical treatment of Twin Reversed Arterial Perfusion (TRAP) sequence aims to interrupt blood flow from the pump twin to the acardiac twin, rather than treating the acardiac twin itself. Stopping this abnormal perfusion reduces the workload on the pump twin's heart and helps lower the risk of high-output cardiac failure and intrauterine fetal death.

   Modern fetal interventions include umbilical cord occlusion, bipolar cord coagulation, laser coagulation, cord ligation, radiofrequency ablation (RFA), and other intrafetal techniques.

   Do All Cases of TRAP Sequence Require Surgery?

   No. Not all cases require surgical intervention.

   If the acardiac twin is relatively small, the pump twin is growing appropriately, and there are no signs of cardiac strain or circulatory overload, close monitoring with ultrasound and Doppler studies may be an appropriate management strategy.

   Intrauterine intervention may be considered when findings indicate an increased risk to the pump twin, including:

3. Significant enlargement of the acardiac twin relative to the pump twin.

4. Increased blood flow to the acardiac twin.

5. Signs of circulatory overload or cardiac dysfunction in the pump twin.

6. Development of fetal hydrops (hydrops fetalis).

7. Increased amniotic fluid volume (polyhydramnios).

8. Significant abnormalities on Doppler assessment of the pump twin.

9. Certain cases of monoamniotic twin pregnancy, particularly when cord-related risks are present.

10. The choice of intervention depends on gestational age, the size of the acardiac twin, the condition of the pump twin, vascular anatomy, the location of the umbilical cord and placenta, and the expertise of the specialized fetal medicine center.

    1. Radiofrequency Ablation (RFA)

    Radiofrequency ablation is one of the most widely used techniques for treating TRAP sequence. It can generally be performed under ultrasound guidance without the need to insert a fetoscope into the uterus.

    Principle of the Procedure

    A specialized probe or electrode is introduced through a needle under ultrasound guidance and positioned within the appropriate area of the acardiac twin, particularly near the vessels supplying it with blood.

    Radiofrequency energy is then applied to produce thermal coagulation of the targeted vessels, interrupting blood flow to the acardiac twin.

    The process can be summarized as follows:

    Pump twin → Interruption of blood flow → Acardiac twin

    This interrupts the abnormal circulation and reduces the cardiovascular workload on the pump twin.

    Recent studies have established RFA as a commonly used technique with high technical success rates. However, its superiority in terms of pump-twin survival over all other occlusion techniques has not been conclusively established.

    Advantages of RFA

11. Usually does not require fetoscopy.

12. Can be performed under ultrasound guidance.

13. May be used at different gestational ages, depending on the clinical situation.

14. Allows direct targeting of the vessels supplying the acardiac twin.

15. Enables ultrasound and Doppler assessment of the pump twin during and after the procedure.

16. Potential Complications

17. Preterm prelabor rupture of membranes (PPROM).

18. Preterm birth.

19. Bleeding or complications associated with needle insertion.

20. Unintentional injury to the pump twin.

21. Incomplete interruption of blood flow in some cases.

22. Need for repeat intervention in a limited number of cases.

23. The procedure may become more challenging when the acardiac mass is very large, fetal hydrops is present, or access to the appropriate vascular target is difficult.

    2. Bipolar Cord Coagulation

    Bipolar cord coagulation aims to occlude the umbilical cord of the acardiac twin directly, thereby interrupting the blood supply it receives from the pump twin.

    How Is the Procedure Performed?

    The umbilical cord of the acardiac twin is identified using ultrasound. A bipolar coagulation instrument is then guided toward an appropriate segment of the cord, either under ultrasound guidance or with the assistance of a fetoscope in selected cases.

    Once the target segment is identified, electrical energy is applied to coagulate the blood vessels within the umbilical cord.

    Following successful occlusion:

    Cord occlusion → Cessation of blood flow → Interruption of reversed perfusion

    This prevents further blood from reaching the acardiac twin and reduces the circulatory burden on the pump twin.

    Main Advantage

    The principal advantage is that the procedure targets the source of the blood supply directly—the umbilical cord of the acardiac twin—rather than targeting vessels within the acardiac twin's body.

    Potential Limitations and Complications

24. Difficulty accessing the cord safely.

25. Technical challenges when the cord is poorly positioned.

26. Need for specialized fetal surgery expertise.

27. Potential bleeding.

28. Preterm prelabor rupture of membranes.

29. Increased risk of preterm birth.

30. Possibility of incomplete occlusion.

31. Bipolar cord coagulation is selected on an individual basis according to cord position and placental and fetal anatomy. No single technique is suitable for every case of TRAP sequence.

    3. Laser Cord Coagulation

    Laser cord coagulation follows a principle similar to bipolar cord coagulation, but it uses laser energy to coagulate the blood vessels within the acardiac twin's umbilical cord.

    Principle of the Procedure

    The umbilical cord of the acardiac twin is first identified. A laser beam is then directed toward the targeted vessels to produce photocoagulation, interrupting blood flow.

    The procedure follows these steps:

    Cord identification → Laser application → Vascular coagulation → Cessation of blood flow → Interruption of reversed perfusion

    Laser-based cord occlusion has been used as an intervention for TRAP sequence. Laser techniques and RFA are among the methods used to interrupt blood flow to the acardiac twin.

    Main Advantages

32. Direct targeting of the umbilical cord.

33. Interruption of the blood supply to the acardiac twin.

34. Potential use of fetoscopy when direct access is appropriate.

35. Avoidance of the need to target deep vessels within the acardiac twin's body.

36. Main Advantages

37. Directly interrupts the source of blood supply.

38. Does not rely on coagulating vessels within the acardiac twin's body.

39. May be an option in selected cases where the cord is readily accessible.

40. Potential Limitations and Complications

41. Technical difficulty when the cord is poorly positioned.

42. Need for specialized fetal surgery expertise.

43. Potential bleeding.

44. Risk of membrane rupture.

45. Increased risk of preterm birth.

46. Some analyses have suggested that certain cord-ligation techniques may carry a higher bleeding risk than RFA. However, comparative evidence remains limited because TRAP sequence is rare.

    7. Fetoscopic Cord Occlusion

    Fetoscopic cord occlusion is not a single treatment technique in itself. Rather, it describes an approach in which a fetoscope is used to access the umbilical cord, allowing an appropriate cord-occlusion method to be performed.

    Principle of the Procedure

    The fetoscope is introduced into the uterus under specialized surgical conditions. The umbilical cord of the acardiac twin is then identified through direct visualization.

    Once the cord has been located, an appropriate technique is used to occlude or coagulate its vessels, depending on the available technology and the anatomy of the case.

    The process can be summarized as follows:

    Fetoscope insertion → Identification of the acardiac twin's cord → Cord occlusion or coagulation → Cessation of blood flow → Interruption of reversed perfusion

    Why Is Fetoscopy Important?

    Fetoscopy provides direct visualization of the umbilical cord and blood vessels rather than relying solely on ultrasound imaging. It may therefore be useful in cases where direct access to the cord is appropriate.

    However, fetoscopic procedures require specialized expertise and carry the risks associated with intrauterine intervention, particularly preterm prelabor rupture of membranes and preterm birth.

    8. Intrafetal Laser Ablation: An Alternative Approach

    Intrafetal laser ablation is distinct from umbilical cord occlusion because it targets the blood vessels supplying the acardiac twin from within its body rather than targeting the umbilical cord.

    Principle of the Procedure

    An appropriate instrument is directed toward the targeted vascular region within the acardiac twin under ultrasound guidance. Laser energy is then applied to coagulate the vessels supplying the twin.

    The process follows these steps:

    Vessels supplying the acardiac twin → Laser coagulation → Cessation of blood flow → Interruption of reversed arterial perfusion

    This technique may be suitable in selected cases in which access to the umbilical cord is difficult, but the internal vessels of the acardiac twin are more accessible based on the anatomical configuration.

    The final choice of treatment should be made by a specialized fetal medicine team after careful assessment of the pregnancy, the pump twin's cardiovascular status, and the technical feasibility and risks of each procedure.

     

    Limitations and Potential Complications

    Successful treatment depends on whether the umbilical cord can be accessed safely. The procedure may be more difficult when the cord is poorly positioned or difficult to visualize.

    As with other intrauterine interventions, complications may include membrane rupture and preterm birth.

    4. Intrafetal or Interstitial Laser Ablation

    Intrafetal laser ablation differs from umbilical cord occlusion because the target is not the cord itself but the blood vessels within the acardiac twin that supply its tissues.

    Principle of the Procedure

    An appropriate instrument is introduced into the targeted vascular region within the acardiac twin under ultrasound guidance. Laser energy is then applied to coagulate the supplying vessels.

    The process can be summarized as follows:

    Vessels supplying the acardiac twin → Laser coagulation → Cessation of perfusion → Interruption of reversed blood flow

    When May This Technique Be Considered?

    This approach may be considered in selected cases where access to the umbilical cord is difficult or unsafe, but the vessels within the acardiac twin can be reached more appropriately based on the anatomy.

    The choice depends on the position and size of the acardiac twin, the location of the cord and placenta, and the experience of the fetal medicine center.

    5. Laser Photocoagulation of Placental Vascular Anastomoses

    This procedure differs from cord occlusion and RFA because it targets abnormal vascular connections between the circulatory systems of the two twins within the placenta.

    Principle of the Procedure

    A fetoscope is used to access and visualize the placental surface and its vascular connections. The abnormal vessels that allow blood to flow from the pump twin to the acardiac twin are identified.

    Laser energy is then directed at the selected connections to produce photocoagulation and close them.

    The procedure follows these steps:

    Fetoscopic visualization of the placenta → Identification of vascular connections → Laser photocoagulation → Interruption of the connection → Cessation of perfusion to the acardiac twin

    This is a specialized intervention requiring considerable fetal surgery expertise because the abnormal vessels must be identified accurately while avoiding damage to vessels essential for the pump twin.

    6. Umbilical Cord Ligation

    Umbilical cord ligation involves mechanically closing the umbilical cord of the acardiac twin to stop blood from reaching it.

    Principle of the Procedure

    The umbilical cord is accessed using an approach appropriate to the clinical situation. It is then mechanically closed using a suitable surgical method.

    The process can be summarized as follows:

    Access to the umbilical cord → Mechanical closure or ligation → Cessation of blood flow → Interruption of reversed perfusion

7. Fetoscopic Cord Occlusion

Fetoscopic cord occlusion is not a single treatment technique in itself. Rather, it is an approach used to access the umbilical cord with a fetoscope, allowing an appropriate cord-occlusion technique to be performed.

Principle of the Procedure

The fetoscope is introduced into the uterus under specialized surgical conditions. The umbilical cord of the acardiac twin is then identified through direct visualization.

Once the cord has been located, an appropriate technique is used to occlude or coagulate its blood vessels, depending on the available technology and the anatomical characteristics of the case.

The procedure can be summarized as follows:

Fetoscope insertion → Identification of the acardiac twin's umbilical cord → Cord occlusion or coagulation → Cessation of blood flow → Interruption of reversed arterial perfusion.

Importance of Fetoscopy

Fetoscopy provides direct visualization of the umbilical cord and its blood vessels, rather than relying solely on ultrasound imaging. It may therefore be useful in cases where direct access to the cord is appropriate.

However, fetoscopic intervention requires specialized expertise and carries risks associated with intrauterine procedures, particularly preterm prelabor rupture of membranes (PPROM) and preterm birth.

Intrafetal Laser Ablation

Intrafetal laser ablation differs from umbilical cord occlusion because the target is not the umbilical cord itself, but rather the blood vessels supplying the acardiac twin from within its body.

Principle of the Procedure

An appropriate instrument is guided into the targeted vascular region within the acardiac twin under ultrasound guidance. Laser energy is then applied to coagulate the vessels supplying the twin, thereby interrupting its blood supply.

The process can be summarized as follows:

Vessels supplying the acardiac twin → Laser coagulation → Cessation of blood flow → Interruption of reversed arterial perfusion.

This approach may be considered in selected cases where access to the umbilical cord is difficult, but the internal vessels of the acardiac twin are more accessible based on the anatomical configuration