Twin to Twin Transfusion Syndrome (TTTS) is a serious complication of an identical twin pregnancy in which there is only one placenta. TTTS occurs in 10-15% of identical twin pregnancies. When TTTS occurs, there is an unequal sharing of blood between two fetuses due to blood vessels that communicate between the two fetuses in the single placenta. In the most serious cases, one fetus (called the Recipient twin) is larger and surrounded by an excessive amount of amniotic fluid, while the other fetus (known as the Donor twin) is smaller and appears to be stuck against the uterine wall due to the reduced amount of amniotic fluid.
In the early stages of the disease, signs include a large amount of fluid around the larger, Recipient twin and a smaller amount of fluid around the smaller, Donor twin. The bladder of the Donor twin may still be seen during an ultrasound examination.
As the disease progresses, the Donor (smaller twin) may no longer have a visible bladder and a very small amount of amniotic fluid or no amniotic fluid. This is referred to as “stuck twin” syndrome, because the smaller twin actually appears to be stuck to the uterine wall or wrapped up in the amniotic membrane (”vacuum packed”).
Ultrasound Doppler studies provide information about the condition of the blood circulation for both of the twins. As the condition worsens, the Donor twin does not receive enough blood and the Recipient receives too much blood.
In the advanced stages, an excessive amount of fluid builds up within the Recipient twin due to heart failure. This is called “hydrops”. Related symptoms include swelling of the skin around the head, swelling of the abdomen (ascites), poor contractions of the heart, and heart failure. Either twin can develop hydrops, but more often it occurs in the recipient twin. The pregnancy may be lost from heart overload in the larger twin, lack of enough blood getting to the smaller twin, or preterm (early) labour because of the excess fluid causing the uterus to be ‘overstretched’.
Diagnosis of TTTS
Diagnosis of TTTS is made if the twin pregnancy fulfills the following criteria:
- Fetuses with same sex
- Single placenta (monochorionic-diamniotic)
- Minimal fluid in donor (less than 2 cm pocket)
- Too much fluid in the recipient (more than 8 cm pocket)
- Thin dividing fetal membrane
- Prominent bladder in recipient
- Absence of other structural problems in either twin
# Please note that the discordance in weight between the babies is not a requirement for the diagnosis of TTTS.
Differential diagnosis of TTTS includes:
- Twins with selective IUGR of one fetus (SIUGR)
- Twins with fetal anomaly
If not treated, severe Twin to Twin Transfusion Syndrome has a mortality rate close to 100%. Current treatment methods include:
- Serial Amnioreduction
- Umbilical Cord Occlusion
- Laser photocoagulation of the communicating vessels
In serial amniocentesis excess fluid is removed from the amniotic sac of the Recipient (larger) twin with a needle. Repeated removal of fluid may be needed. Each time fluid is removed; 1-4 litres may be obtained. How often fluid is withdrawn depends upon how severe the case. It may need to be done as often as every second day.
The success rate (at least one survivor) for this technique varies, but may be as high as 60-70 %.The advantage of serial amniocentesis is that it may prevent pre-term labour and thereby extend the pregnancy for a few more weeks. The main disadvantages of this approach are that it does not fix the basic problem (unequal sharing of blood), therefore making repeat removal of fluid necessary, each with its own risk of trauma, infection, or pregnancy loss. If one baby dies from the disease, the shared blood flow between the babies may allow for the second twin to bleed into the dead twin. This may cause death (up to 40%) or brain or neurological damage (15 – 25%). Serial amniocentesis may also cause the membranes to detach from the uterine wall. This may make any other form of invasive intrauterine therapy more difficult. Furthermore the success rate with this method is poor when the disease is severe (Stages III & IV – see below for staging of the severity of the disease). Pregnancies that develop signs of TTTS after 26 weeks gestation are usually managed by serial amniocentesis as the fetuses are at a viable age.
This procedure consists of purposely disrupting the dividing membrane between the fetuses with a needle. This results in equalization of the fluid volumes between the sacs. There is little data to support this therapy. Moreover, the disruption of the membrane may lead to death of the fetuses from cord entanglement.
3) Umbilical Cord Occlusion
In severe cases of TTTS, one of the fetuses may be extremely sick at the time of presentation. Attempts to save both fetuses in this case may be futile, as the sicker fetus may die despite all efforts. Spontaneous death of the unhealthy fetus may in turn cause death or neurological damage to the co-twin. An umbilical cord occlusion may be performed to save the co-twin from harm. The chance of miscarriage following this procedure is about 10%. Umbilical cord occlusion is offered only in severe cases and the intent is to save the life of the other twin.
4) Laser Photocoagulation of Communicating Vessels
Laser surgery may be performed to stop the sharing of blood between the two fetuses. The object of this method is to treat TTTS by laser coagulating the specific vessels that cause the problem of blood sharing in this syndrome and spare the remainder of the vessels. The laser is used to seal the vessels to stop the blood flow between the fetuses. Overseas centers report a 85% survival rate for at least one baby and 50 to 75% for both, with an incidence of neurological complications of 2 to 5%.
The surgery can be done under general anesthesia or local anesthesia. A small incision (1cm) is made in the mother’s belly to insert a fetoscope and laser fiber, under combined ultrasound and fetoscope guidance. The fetoscope is a long, narrow telescope with a light and camera on the end. The blood vessels are identified and sealed through the fetoscope. The purpose of surgery is to separate the circulation between the babies by using the laser to seal the vessels connecting the two. In essence, these babies are now like fraternal twins. They are no longer sharing blood and each has its own portion of the placenta.
The main advantage to this method is that the disease is corrected in the majority of cases with a single treatment even for the more severe stages of the disease (Stage III & IV). In addition, cerebral palsy and other complications caused by the death of one of the twins are less likely to occur (approximately 5%) than with serial amnioreduction. If one fetus dies, the other twin is not likely to be affected.
Criteria for Laser Photocoagulation for TTTS
Patients are considered for laser photocoagulation when the pregnancy is between 18 and 26 weeks gestation and fulfill the following criteria:
- Both the fetuses are of the same sex
- Single placenta (monochorionic diamniotic)
- Minimal fluid in donor (less than 2 cm maximal vertical pool)
- Too much fluid in the recipient (more than 8 cm maximal vertical pool)
- Thin dividing fetal membrane (this may be sometimes too thin to see)
- Absent bladder in the donor twin or absent/reversal of end diastolic flow in the umbilical artery
- Absence of other structural problems in either twin
A patient may not be offered this procedure if the following conditions exist:
- Abnormal genetic studies (if a karyotyping was done earlier)
- Ruptured or detached membranes
- Prior septostomy (purposely making a hole in the dividing membrane )
- Short or dilated cervix
- Pre-term labour
Risks and Complications
There are potential complications associated with this procedure:
- There is the possibility of bleeding in the mother and/or fetuses, which could prevent the completion of the procedure.
- Rarely, bleeding may be of such magnitude that we may need to make an abdominal incision (laparotomy) and place a suture on the uterus.
- Preterm labor, amniotic fluid leakage or premature rupture of membranes could occur. If any of these complications occur, we may need to keep the mother in the hospital. Infection of the amniotic cavity may also occur and lead to these complications. If infection is diagnosed, delivery is required to prevent further complications.
- Placental abruption or separation has been rarely reported
There is a low incidence of these complications as precautions are taken to minimize these risks. Patients are placed on antibiotics to prevent infection. Very small instrumentation is used to help prevent bleeding and preterm labour. All patients are evaluated thoroughly prior to this procedure.
Staging of TTTS
Staging of TTTS is based on ultrasonographic and Doppler findings using the Quintero staging classification. TTTS is staged in an effort to offer the most appropriate treatment for the level of disease present. Laser treatment may not be indicated in all cases.
In Stage I there is a small amount of fluid (oligohydramnios) in the donor and a large amount of fluid (polyhydramnios) in the recipient. At this stage, laser treatment may not be indicated but close observation for a change in condition is recommended.
In Stage II, along with poly/oligohydramnios, there is no visible bladder in the donor. At this stage, laser treatment is considered.
Stage III is characterized by Critically Abnormal Dopplers (Absent or reversal of end diastolic flow of the umbilical arteries), which means one of the babies has abnormal blood flow. Laser treatment is offered for this stage. If laser treatment is not possible, umbilical cord occlusion may be performed if absolutely necessary.
In Stage IV, all of the above findings are present and the baby is hydropic. This means that there is swelling of the head and abdomen (ascites), the heart contracts poorly, and heart failure is present.
|Stage||Poly/Oligo||Absent Bladder||Absent or reversal of umbilical artery||Hydrops||Demise|
What do I need to do as a referring centre?
- 1. Identify the monochorionic diamniotic pregnancies early
As TTTS is linked to monochorionic placentation, early diagnosis of chorionicity before 15 weeks is crucial, but feasible only by ultrasound examination. The steps in determining placentation include determination of gender, visualization of the placental mass and characterization of the dividing membrane. The same gender, a single placental mass and a thin, wispy membrane that cleanly joins the chorionic plate of the placenta – the so-called ‘T’ sign – make monochorionic–diamniotic placentation most likely (Please visit www.japaraj.com for ultrasound clips on diagnosis of monochorionicity and TTTS).
- 2. Follow up and diagnose TTTS early
Once a multiple pregnancy has been diagnosed to be monochorionic diamniotic, the patient will have to be seen regularly (if possible every 2 weeks and preferably by a MFM specialist) so that early diagnosis of TTTS can be made.
- 3. Refer the TTTS cases which fulfill criteria for laser treatment to the Maternal Fetal Medicine unit
Once the patient has been identified as having TTTS, is in stage II to IV (Quintero classification) and is between 18 to 26 weeks gestation, please counsel the patient about her condition using the Patient Information Sheet which includes information on the disease, prognosis and available treatments and the option of laser treatment and its risks and complications. The final decision of whether the patient is suitable for the laser treatment will be made by the MFM consultant. Referral to hospital does not automatically mean that the patient will have laser treatment as many a time the patient may have a misdiagnosis or the patient may have progressed to a worse stage of TTTS which is not amenable to laser treatment.
What happens to patients who undergo laser treatment for TTTS?
Pretreatment: After the patient is seen and evaluated by the MFM consultant in hospital, extensive counseling is given to the patient with regards to the procedure and what it can and cannot achieve. The patient will be admitted to hospital the night before the procedure. She will be fasted the night before the procedure. The patient is given prophylactic dose of antibiotics and oral tocolysis (nifedipine) just before the procedure. An ultrasound will be done prior to going to the operating room to confirm the babies’ heartbeats.
The laser procedure: The procedure will usually be done under sedation and local anesthesia. The procedure usually lasts around 2 to 3 hours (from the time the patient is wheeled into the OT till the patient leaves).
Post treatment: After the procedure, the patient is rested in the High Risk Antenatal Ward for 1 day. A repeat ultrasound is done to assess the wellbeing of the fetuses. If the patient has preterm contractions, she will be treated with oral nifedipine. The patient is usually discharged the day after the procedure if there are no complications. She can be followed up at her local tertiary centre on a regular basis (2 weekly if possible) and subsequently delivered in that centre. The recommended gestation of delivery for uncomplicated cases of post laser treated TTTS is 36 to 38 weeks. Most of them will need delivery via LSCS.
Can twins with other problems have laser photocoagulation treatment?
Yes. Apart from TTTS, laser photocoagulation may be offered to pregnancies affected by acardiac twin (TRAP sequence) following assessment by the MFM consultant.
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