Twins / Multiples | Selective Intrauterine Growth Restriction (sIUGR)

Although twins that share a placenta (monochorionic) are often referred to as “identical” twins, they may behave very differently while still inside the womb. Sometimes, there are imbalances in the way the fetuses share the placenta, resulting in one twin thriving while the other receives less nutrition and grows poorly. Occasionally, one twin will develop a structural abnormality that is not found in the other. In cases such as these, where there are differences in the structural makeup or growth of one twin, a fetal therapy may be warranted to improve the survival chances of the healthy twin.

Essential Information

  • In cases where monochorionic twins do not share their placenta equally, one fetus may grow normally while the other may be much smaller.
  • In severe cases, the smaller fetus may pass away suddenly, and, because monochorionic twins share placental circulations, the other fetus risks severe disability or even death.
  • In some cases, one twin may develop abnormally, with problems seen in major organs that can impact its ability to survive outside the womb.
  • In severe cases where there is a concern that the smaller or unhealthy twin may pass away suddenly inside the womb, a fetal procedure may be offered to interrupt the blood flow to the sick fetus before it passes away suddenly. This improves the chances that the healthier fetus will survive.

Overview

Although twins that share a placenta (monochorionic) are often referred to as identical twins, they may, in fact, behave very differently while still inside the womb. Sometimes, there are imbalances in the way the twins share the placenta, resulting in one twin thriving while the other receives less nutrition and grows poorly. In these cases, the smaller, or growth-restricted, twin may have low amniotic fluid levels and abnormal blood flow patterns in its umbilical cord. Differentiating this condition from twin-twin transfusion syndrome (TTTS), another common complication in monochorionic twins, is challenging, and therefore, if suspected, close surveillance with ultrasound in the hand of experts is key.

Occasionally, one twin will develop a structural abnormality that is not found in the other. These abnormalities may affect essential organs such as the heart or the kidneys, and may threaten this twin’s ability to survive both inside and outside the womb.

Because monochorionic twins share placental circulations, the sudden death of one can result in severe disability or death in the other. Very close surveillance with ultrasound is important so as to identify signs of difficulty in the smaller or unhealthy twin. In some cases, interrupting the blood flow to the sick twin may be offered so as to prevent its sudden death and improve the survival and outcomes of the other.

 

Treatment

Close surveillance with ultrasound is critical so as to identify signs of struggle in the smaller twin, and so as to differentiate this presentation from other complications of monochorionic twin pregnancies. Occasionally, admission to hospital for close monitoring may be required.

In some cases, a fetal therapy aimed at interrupting the sick twin’s blood flow using radiofrequency energy (termed “radiofrequency ablation (RFA)”) may be offered. This procedure is intended to prevent the sudden death of the sick twin so as to improve the survival and outcomes of the other healthy twin.

Referral Information (for physicians)

Inclusion criteria:

Monochorionic multiple pregnancy with severe fetal anomalies or severe selective intrauterine growth restriction with a moribund smaller fetus (reversed end-diastolic flow in umbilical artery, abnormal flow in ductus venosus, arrest of growth, oligohydramnios or anhydramnios, or empty bladder).

Practically:

Patient eligibility, surgical feasibility, timing of surgery and surgical technique will be determined on a case-by-case basis. Hospitalization is typically less than 24 hours. Patients will be referred back to their local provider for further follow-up and delivery.