What is Twin to Twin Transfusion Syndrome?
Twin to Twin Transfusion Syndrome or TTTS, is a serious complication of the placenta in identical twin/multiples pregnancies. It occurs when the blood vessels from each twin become interconnected in the placenta and the blood flow becomes unbalanced.
One twin then receives too much blood and nutrients (called the recipient) and the other does not get enough (called the donor). This means that the recipient twin starts to produce too much fluid, and the donor twin does not produce enough. This can cause serious problems, or worse, death of one or both twins.
How Often Does TTTS Occur?
Approximately 10-15% of shared placenta (Monochorionic-Diamniotic or Mono/Di and Monochorionic-Monoamniotic or Mo/Mo) pregnancies will face TTTS.
What Is The Survival Rate?
If left undiagnosed and untreated TTTS has a survival rate of +/- 10%. But when monitored and with appropriate medical intervention the survival rate can improve to 70% or better.
How Often Should I Be Checked for TTTS?
The latest research supports checks every 2 weeks from 16 weeks being successful in finding 90% of TTTS cases in time to treat them. Your doctor may want to monitor you more closely - and that's also fine. Make sure you check your insurances so you don't get any out-of-pocket surprises though! A good idea is to have a discussion with your team about what will happen if you are diagnosed with TTTS, when they will refer you to a fetal surgeon, and also where they will refer you. While it is only a 10-15% chance of developing TTTS, it's a good idea to have an action plan ... just in case.
TTTS Warning Signs
There are warning signs for TTTS. The pregnant person may feel like their belly got larger all of a sudden, or they gained weight rapidly. Other signs can be things like feeling your belly skin is super stretched, cramping/contractions, fluid retention, lack of movement, and just feeling heavy overall. If you are pregnant with monochorionic twins, and you experience these symptoms, go immediately to get checked out.
TTTS Staging System
Twin-twin transfusion syndrome is diagnosed using a staging system, with the most widely recognized being the Quintero Staging System. Introduced in 1999, this staging system is used today, although many variations of this system are also adopted worldwide. For example, in a lot of centers in Europe, after 20 weeks more than 10cm of fluid is used as the cutoff point for stage 1, thanks to the findings of the Eurofetus trial. Research is continually evolving, and it's important to discuss with your care team how they stage TTTS, and also when they will intervene.
Quintero Staging - Donor fluid less than 2cm, Recipient fluid more than 8cm PLUS
- Stage I: The fetal bladder of the donor twin remains visible sonographically.
- Stage II: The bladder of the donor twin is collapsed and not visible by ultrasound.
- Stage III: Critically abnormal fetal Doppler studies noted. This may include absent or reversed end-diastolic velocity (flow) in the umbilical artery, absent or reverse flow in the ductus venosus (liver), or pulsatile flow in the umbilical vein.
- Stage IV: Fetal hydrops present.
- Stage V: Demise of either twin.
Between 16 weeks, and 28 weeks, laser surgery using either the Selective Laser Ablation technique, or the Solomon Technique is the most effective treatment for TTTS. Amnioreduction is used as well, but is falling out of favor.
It's important to discuss this as an option with your care team, and find a surgeon that works with you for this.
In the US, the Fetal Health Foundation can provide support and advice on the surgeons that are closest to you. Within Australia, check your local team and where they refer to, as most states have a specialist center for treating TTTS, and in New Zealand this is located in Auckland Hospital . In the UK, your consultant will refer you to the tertiary center that is closest to you and works with your trust, but you can also consult with the Twins Trust.
Long Term Outcomes of TTTS
TTTS survivors do show signs of neurodevelopmental impairment. This is generally defined as cerebral palsy, blindness, deafness, cognitive/developmental delays, etc. There is no difference in outcomes for donors and recipients.
In cases treated by amnioreduction only, up to 20% (or 1 in 5) cases will show signs of severe neurodevelopmental impairment. When treated with laser surgery this reduces down to a 10% chance, or one in 10. Prematurity is a major contributor to complications for these twins as well.
For all survivors, long term followups are essential so that early intervention can be made. Development checks should be done up to school age.
Call to action: long-term neurodevelopment in monochorionic twins - Khalil et al (2021)
Longitudinal Follow-Up of Children Born Preterm: Neurodevelopment From 2 to 10 Years of Age - Jansen et al (2021)
Long-Term Neurodevelopmental Outcome in Survivors of Twin-to-Twin Transfusion Syndrome - van Klink et al (2016)
Long-Term Neurodevelopmental Outcome in Twin-to-Twin Transfusion Syndrome: Is there still Room for Improvement? - Spruijt et al (2019)
Neonatal management and outcome in complicated monochorionic twins: what have we learned in the past decade and what should you know? - Groene, Tollenaar et al (2022)
- Fetal Health Foundation - Twin-Twin Transfusion Syndrome
- Twins Trust - TTTS