Monochorionic monoamniotic twins – Mechanism, Incidence, Complications, Diagnosis and Management

Monochorionic monoamniotic placenta with cord entanglement
Click on image for an enlarged view

Monochorionic monoamniotic twins have single placenta and lie in a single amniotic cavity.

Mechanism:

  • It arises from division of the implanted blastocyst 8-13 days after fertilisation
  • Division of blastocyst beyond this period results in conjoint twins

Incidence:

  • It occurs in 1 in 35000 to 1 in 60000 pregnancies
  • It constitutes 1% of monozygotic pregnancies

Complications:

  • High risk of cord entanglement – up to 71% (more than 50% of perinatal deaths occur due to this)
  • Cord compression – one twin may compress the cord of the other
  • Twin – twin transfusion syndrome

Diagnosis:

  • Ultrasound scan
    • Single placenta
    • Absence of inter twin dividing membrane
    • Single yolk sac (in most cases)
    • Concordant gender
    • Cord entanglement later in pregnancy

Management:

  • Regular foetal monitoring
  • Check for development of complications
  • Early termination of pregnancy by caesarean section by 32-34 weeks
    • There is increased incidence of cord entanglement after this period
  • Steroid administration to promote foetal lung maturity
  • Maternal sulindac (selective COX2 inhibitor) has been tried to reduce amniotic fluid volume and thereby risk of cord entanglement

Image credits: Rinoop Ramachandran, Calicut Medical College

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