Twin to Twin transfusion: What is it?

Twin-to-twin transfusion syndrome (TTTS) is a rare condition that may affect identical twins who share a common placenta (monochorionic twins). It is a condition in which the blood flows unequally between the two babies that share a placenta (monochorionic twins).

TTTS occurs in about 10 to 15 percent of monochorionic, diamniotic (two amniotic sacs) twins. It is essentially a plumbing problem in the placenta. Approximately 20% of all twin pregnancies are monochorionic, fraternal twins are not at risk for this syndrome because they do not share a placenta.

One twin (called the donor twin) pumps blood to the other twin (called the recipient). This causes the recipient twin to receive too much blood and the donor twin to receive too little. The increased volume of blood causes the recipient twin to produce more than the usual amount of pee, can cause a large bladder, too much amniotic fluid, and hydrops, a prenatal form of heart failure. The donor twin, who receives too little blood, produces less than the usual amount of pee. This results in low or no amniotic fluid surrounding it and a small or absent bladder.

Your healthcare provider may suspect this disorder if any of the following is seen during an ultrasound:

  • A significant difference in the size of babies of the same gender
  • Difference in size between the two amniotic sacs
  • Difference in size of the umbilical cords
  • A single placenta
  • Evidence of fluid build up in the skin of either babies
  • Polyhydraminos (excess amniotic fluid) in the recipient twin
  • Oligohydraminos (decreased or too little amniotic fluid) in the donor twin

Without intervention, the condition can be fatal for both twins.The Twin to Twin Transfusion Syndrome Foundation recommends that weekly ultrasounds be performed after 16 weeks through the end of the pregnancy to monitor TTTS. If your Obstetrician suspects you may have TTTS you will be referred to a tertiary care centre where a Maternal Fetal Medicine Obstetrician will perform an ultrasound and assess if TTTS is present.

There are 5 stages of TTTS:

Stage 1:

Polyhydramnios (too much amniotic fluid) in the recipient sac, oligohydramnios (little or no amniotic fluid) in the donor sac

Stage 2:

Donor bladder is not filling and emptying

Stage 3:

Abnormal blood flow patterns, including:

  • Absent/reversed umbilical artery end-diastolic velocity (UAEDV)
  • Reverse flow in ductus venosus (DV)
Stage 4:

Hydrops, or massive fluid retention that puts both mother and twins at risk

Stage 5:

Death of one or both twins while still in the uterus


Treatment for twin-twin transfusion syndrome may include any of the following:

Fetoscopic laser ablation   

it is performed on the placenta to disconnect the communicating blood vessels. This procedure stops the sharing of blood from the donor to the recipient, with the goal of stopping the progression of twin-twin transfusion syndrome. This procedure involves making small incisions in the mother’s skin (called “laparoscopic” or “minimally invasive surgery”), introducing a small camera and then, using a laser beam to interrupt (or burn) the abnormal blood vessel connections in the placenta. The excess amniotic fluid is also drained from around the recipient twin. This is typically the preferred treatment for TTTS, depending on gestational age at presentation, location of the placenta and stage of TTTS. After the procedure, the donor twin may resume making urine and will produce amniotic fluid again. The recipient’s heart, may, in time, recover.

To the best of our knowledge, placental laser surgery results in the highest numbers of healthy survivors in those patients with diagnosis or onset of TTTS less than 25 weeks gestation.  Reports on this therapy currently indicate the following: 80-85% survival of at least one twin, 65-70% overall twin survival, 5% or less significant handicap rates in the survivors, and a treatment to delivery average interval of close to 10 weeks.

Women are fully awake during the procedure, being given sedation from the anesthesiologist. They can watch as much or as little of the procedure as they wish, and the partner is allowed to be in the room for the procedure. This is by far the safest for mom.


Removal of excess amniotic fluid from the larger twin (recipient) which may help ease any pain or discomfort experienced by the mother due to fluid buildup. This is a temporary treatment option and may need to be repeated.

If you are experiencing TTTS in your pregnancy, there are many support groups available on social media and the internet. Speak to your Obstetrician about linking you to resources and other TTTS families.

Contact your local Mama Coach for ongoing support throughout your pregnancy and a private prenatal class customized to your twin pregnancy. We’re here for you Mama!


Womens and Infants Health


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