Prevalence:

• 10-15% of monochorionic twins.

Ultrasound diagnosis:

• There is imbalance in the net flow of blood across the placental vascular communications from one fetus, the donor, to the other, the recipient.
• 11-14 weeks: early TTTS is suspected if there is discordance in size of the amniotic fluid sacs, ≥20% discordance in fetal nuchal translucency (NT) thickness, or absent / reversed end diastolic flow (EDF) in the ductus venosus usually in the fetus with higher NT.
• ≥15 weeks: oligohydramnios (deepest vertical pool of ≤2 cm) in the sac of the oliguric or anuric donor fetus and polyhydramnios (≥6 cm at 15-17 weeks, ≥8 cm at 18-20 weeks and >10 cm at ≥20 weeks) in the sac of the polyuric recipient.
• The condition is subdivided into 4 stages according to the Doppler finding of EDF in the umbilical artery and ductus venosus of both fetuses:
  • Stage 1: donor bladder visible, EDF positive in both vessels in both fetuses.
  • Stage 2: donor bladder not visible, EDF positive in both vessels in both fetuses.
  • Stage 3: EDF absent or reversed in either vessel in either fetus.
  • Stage 4: presence of ascites or hydrops in either fetus; usually the recipient.

Associated abnormalities:

• The incidence of chromosomal abnormalities or genetic syndromes is not increased.

Investigations:

• Detailed ultrasound examination.
• Ultrasound scans every 1 week to monitor growth, amniotic fluid volume and pulsatility index in the umbilical artery, middle cerebral artery and ductus venosus of both fetuses.

Management:

• Discordance in amniotic fluid (but not sufficient to fulfill the oligohydramnios / polyhydramnios sequence) with normal fetal Doppler:
  • Overall survival: 95%.
  • Progression to TTTS: 15%.
  • Ultrasound scans every 1-2 weeks to monitor evolution.
• Stage 1:
  • Survival: overall 85%, at least one twin 90%.
  • Progression to stages 2 to 4: 20%.
  • Ultrasound scans every 1 week to monitor evolution.
  • Endoscopic laser ablation of communicating placental vessels if progression to stages 2-4 or increasing polyhydramnios and shortening of cervical length.
• Stages 2-4:
• <28 weeks: the best management is endoscopic laser ablation of communicating placental vessels; all communicating vessels should be ablated and the area between them should also be coagulated to achieve dichorionization of the placenta.
• ≥28 weeks: the best option is to deliver by cesarean section and the timing would depend on the Doppler findings in the umbilical artery and ductus venosus of both fetuses.
• Stage 2: survival overall 75%, at least one twin 85%.
• Stages 3 and 4: survival overall 60-70%, at least one twin 75-85%.
• Neurodevelopmental impairment in survivors: 5-10%.
• Follow-up after laser therapy: ultrasound scans and Doppler every 1 week until resolution of the signs of TTTS and normalization of Doppler findings and every 2 weeks thereafter with special attention for signs of brain damage, recurrence of TTTS and development of TAPS.
  • Normalization of amniotic fluid volume occurs after 1 week. Resolution of cardiac dysfunction in the receipient and of hydrops in stage 4 TTTS usually occurs after 3-4 weeks.
  • In about 1 in 1,000 cases there may be limb amputation due to thrombotic events or amniotic bands.

Delivery:

• Vaginally at 37 weeks if there is normal growth and Dopplers in both babies.

Recurrence:

• No increased risk of recurrence.