Single Fetal Demise In Twin Pregnancy - Causes And Consequences

What Is Single Fetal Demise in Twin Pregnancy?

The number of multiple pregnancies has increased over time due to assisted reproduction techniques and ovulation induction drugs. Single fetal demise during the first trimester of twin pregnancy is very common and does not have serious consequences. However, single fetal death during twin pregnancy increases the risk of morbidity and mortality of the surviving co-twin.

Based on the timing of a single fetal demise during a twin pregnancy, it can be classified as follows-

• Vanishing Twin Syndrome - This occurs in the first trimester of pregnancy. It can be considered a form of miscarriage. Initially, two fetuses are diagnosed in early ultrasound, but over time, in subsequent ultrasounds, only one fetus can be seen. The fetus that could not sustain life is termed the 'vanishing twin.' After the vanishing twin disappears, its fetal tissues are reabsorbed inside the mother's womb.

• Antepartum Single Twin Demise - This occurs in the second or third trimester of pregnancy. This is a much more severe condition as it predisposes the surviving co-twin to a higher risk of morbidity and mortality. Single twin demise after 17 weeks of gestation (mid-pregnancy) can lead to complications like-

  • Intrauterine growth restriction (IUGR) - Improper growth of existing co-twin.

  • Pre-eclampsia - high blood pressure during pregnancy.

  • Preterm labor.

  • Perinatal mortality - It can be stillbirth (fetal death) or early neonatal death (ENND), which is the death of the newborn in the first seven days after birth.

What Are the Causes of Single Fetal Demise in Twin Pregnancy?

Reasons for a single intrauterine demise can be as follows-

1. Maternal Reasons-

• Preeclampsia.

• Thrombophilia (increased risk of blood clotting).

• Diabetes.

2. Fetal Reasons-

• Infection.

• Chromosomal abnormality.

• Cord entanglement- seen mostly in monochorionic-monoamniotic (momo) twins.

• Velamentous cord.

• Structural anomaly.

• Placental insufficiency.

• Twin-twin transfusion syndrome (TTTS).

• Selective intrauterine growth retardation.

What Is the Effect of Single Fetal Demise on Its Co-twin?

The surviving co-twin is at potentially high risk, mostly for the same pathophysiological reasons that caused the death of one fetus. Other factors that impact the survival of co-twin are-

• Timing - If the single fetal demise occurred in the first trimester, then no adverse outcomes can be expected, but if it occurs during the second or third trimester, there are increased chances of premature delivery, cerebral palsy, or even death.

• Chorionicity - when one twin dies, chorionicity is the prime determinant of the outcome. In dichorionic (DC) pregnancies, twins do not share any placental circulation, and so the twins are hemodynamically independent. Thus, the risk of complications is comparatively lower. Monochorionic (MC) pregnancies are at higher risk as the twins share the placental circulation. Damage to the monochorionic co-twin after the death of one twin can be explained by the following theories-

  • Thromboplastin Theory - This theory says that the thrombotic material from the dead twin passes on to the surviving twin resulting in thromboses and neurological injuries.

  • Ischaemic Theory - This theory says that immediately before death, the fetus becomes hypotensive and partially drains its co-twin by placental anastomoses, resulting in anemia, hypotension, and hypoperfusion for the surviving co-twin.

• Neurological Disorders - After the demise of a single fetus, the surviving co-twin can develop various neurological disorders. These disorders can be seen in the co-twin as early as six days to six weeks after the fetal loss. Some commonly occurring neurological conditions are-

• Cerebral Palsy - A disorder of movement or muscle tone by birth.

• Periventricular Leukomalacia - A type of brain injury that affects premature babies.

• Multicystic Encephalomalacia (MCE) - A condition where brain cells are replaced by cysts.

• Porencephaly - Cysts filled with cerebrospinal fluid present in the brain.

• Hydranencephaly - Characterized by neurological deficits and an enlarged head.

• Microcephaly - Characterized by a smaller size of the head.

What Is the Management of Single Fetus Demise in Twin Pregnancy?

• Early Pre-viable Cases - When a single fetus demise of twin pregnancy takes place in the first trimester, nothing much needs to be done. The fetal tissues of the dead twin are reabsorbed within the body, and no harmful consequences are observed on the living twin. However, there are chances of preterm delivery.

• Late Viable Cases - When a single fetus demise of twin pregnancy takes place in the second or third trimester, much more complications can be expected.

The management of different types of twin pregnancies is as follows,

• Monochorionic - In these cases, the surviving twin has the risk of preterm delivery or ischaemic brain damage or intrauterine death. The best way to prevent damage to living co-twin is immediate delivery after the single fetal demise.

• Dichorionic - The main risk associated with dichorionic twin pregnancies is preterm delivery. Regular fetal and maternal surveillance for hypertension, pre-eclampsia, and disseminated intravascular coagulation is suggested.

• Fetal Surveillance -

  • Ultrasound - Ultrasound is performed to determine the chorionicity and for a thorough examination of the surviving twin. Regular ultrasound of the surviving fetus's brain is done to look for signs of any injury.

  • Magnetic Resonance Imaging (MRI) - MRI screening of a surviving fetus is done to check the presence of any hemorrhage or intracranial injury.

  • Fetal Blood Sampling and Intrauterine Transfusion - After the death of one fetus, the surviving twin has a risk of anemia or hypoxic tissue damage due to hemodynamic changes. Thus, fetal blood sampling of surviving co-twin is done within 24 to 48 hours of fetal death to check for hemoglobin, fetal hematocrit, and acid-base balance of the survivor.

• Gestation of Delivery - If a single fetal demise occurs before 34 weeks of gestation and the lungs of surviving co-twin are yet to develop, then a course of Betamethasone is given to promote lung development.

• Mode of Delivery - Vaginal deliveries can be done, but cesarean section deliveries are recommended to avoid risks.

• Post Delivery - After the delivery, a full examination of the baby should be done. Neurological examinations like cranial ultrasound and MRI are recommended. The baby should be monitored regularly to reach normal milestones. If the cause of single fetal demise in twin pregnancy is not known, then placental examination must be done post-delivery.

• Maternal Monitoring Regular blood pressure monitoring and urine analysis are required to rule out the related risks. Maternal counseling is required to avoid postnatal depression.

Conclusion:

The outcome of a single fetal demise in twin pregnancy depends on the gestational age and the chorionicity. The management of single fetal death in a twin pregnancy can be difficult, so identification of the cause, monitoring the surviving co-twin, deciding the mode and timing of delivery, and maternal counseling are essential factors in determining the prognosis. Parents must be counseled to relieve the grief and guilt of the loss of one baby, and they must celebrate the birth of the surviving baby.