Twin-to-twin transfusion syndrome

Twin to twin transfusion syndrome (TTTS) is a potential complication that can occur in a monochorionic twin (either MCDA or MCMA) pregnancy. 

Epidemiology

This complication can occur in ~10% (range 15-25%) of monochorionic pregnancies giving an estimated prevalence of ~1:2000 of all pregnancies.

Clinical presentation

Marked abdominal distension has been described as a clinical feature.

Pathology

TTTS results from an unbalanced arterio-venous (AV) communication in the placenta with increasing evidence implicating asymmetric anastomotic patterns in its aetiology.

The smaller twin that pumps away blood is termed the donor twin while the larger twin receiving extra blood is termed the recipient twin.

Staging

The extent of the syndrome can be staged according to severity. One method proposed by Quintero et.al is as ³:

• stage I: visible bladder in donor twin with normal Dopplers
• stage II: empty bladder in donor twin with normal Dopplers
• stage III: empty bladder in donor twin with abnormal Dopplers
• stage IV: hydrops fetalis in recipient twin
• stage V: demise of any twin

Variants

• twin anaemia-polycythaemia sequence (TAPS)

Radiographic features

Antenatal ultrasound

General features that may suggest towards the diagnosis include:

• twin growth discordance between the two twins (>20%)
• there may be folding of the inter-twin membrane as an early sign due to disparity in amniotic fluid volumes (amniotic fluid discordance)
• in early pregnancy, there may be a difference in nuchal translucency between the twins
• significant difference in umbilical cord diameter

Features that may noted individually in each twin include:

• recipient twin
  • is larger in size and will have an increased estimated fetal weight (EFW)
  • polyhydramnios
  • large urinary bladder
  • evidence of fetal polycythaemia
  • fetal hydrops
  • fetal cardiomegaly
    • in certain cases fetal echocardiography may also show AV valve incompetence
• donor twin (pump twin / stuck twin)
  • the small twin (with decreased EFW) can appear "pinned" to side of gestational sac
  • evidence of fetal anaemia
  • oligohydramnios
  • small/ absent urinary bladder

Possible predictors in first trimester ultrasound :

• presence of monochorionicity
• increased nuchal translucency and/or disparity in nuchal translucency between the twins
• poor crown-rump length growth of one fetus
• membrane folding at 10-13 weeks of gestation
• velamantous cord insertion

Doppler

• absent or reversed diastolic flow in the umbilical artery is an indication of worsening twin-to-twin transfusion syndrome
• abnormal ductus venosus waveform pattern suggests possibility of cardiac diastolic dysfunction 

Treatment and prognosis

TTTS generally carries a poor prognosis. Serial sonographic monitoring is often common practice. Laser coagulation of the chorionic plate has been trialled as a management option. Other possible interventions include:

• amnioreduction in recipient twin
• septostomy
• maternal digitalis therapy 

Differential diagnosis

General considerations include:

• placental insufficiency in one of the twins: will not produce polyhydramnios in opposite twin