Intrauterine fetal demise of one twin
1. What every clinician should know
Multifetal pregnancies are associated with a higher risk of perinatal morbidity and mortality when compared with singleton pregnancies. The incidence of single fetal death in twin pregnancies is 2.5% to 5.0 % as compared to 0.3% to 0.6% in singletons. Intrauterine fetal demise of a single twin can have profound consequences for the co-twin including an increased risk of preterm birth, neurologic morbidity, and an increased risk of mortality.
Single fetal death is common in early pregnancy, with report of a vanishing twin occurring in as many as 21% of early twin pregnancies. This usually results in a good outcome for the surviving fetus, though long-term neurologic outcome studies are lacking.
Although risks can affect the co-twin survivor in both dichorionic and monochorionic gestations, due to placental vascular anastomoses, intrauterine death of a monochorionic twin is associated with increased morbidity and mortality in the surviving co-twin. One previous study described a 12% risk of co-twin death in monochorionic twins as compared to a 4% risk in dichorionic pregnancies.
2. Diagnosis and differential diagnosis
Factors that lead to the intrauterine death of one fetus may also affect the well-being of the co-twin. These include twin-twin transfusion syndrome, congenital anomalies, abnormal cord insertion or intrauterine growth restriction. There also may be significant maternal morbidities affecting both fetuses. The patient may report decreased fetal movement, prompting sonographic evaluation, or it may be diagnosed unexpectedly during routine antenatal testing.
As chorionicity will ultimately determine the risk of morbidity and mortality to the co-twin, an ultrasound performed at the initiation of prenatal care will subsequently aid in counseling the patient and management of the remaining fetus.
Mode of delivery will depend on the presentation of the live fetus, the gestational age and indication for delivery and the intrapartum fetal heart rate tracing of the remaining fetus. Intrauterine co-twin demise is not an indication alone for cesarean delivery; however, many other factors need to be considered prior to recommending the optimal mode of delivery.
Neonatal imaging are recommended, especially for all neonates that were monochorionic. In the cases of unknown chorionicity, placental analysis and vascular mapping may be performed. Close developmental assessment and follow-up are recommended throughout infancy and early childhood.
As mentioned previously, single fetal death after 20 weeks of gestation occurs in approximately 5% of twin pregnancies. Because of the presence of placental anastomoses between monochorionic twins, the death of one twin can cause an acute hypotension, anemia and ischemia in the co-twin thought to be a result of the acute shunting of blood to the demised fetus. In a dichorionic pregnancy, these vascular anastomoses are not present, but the intrauterine environment that may have caused the initial fetal demise–infection, maternal medical disease–may place the surviving twin at risk as well.
Unfortunately, the changes that occur within the placental and fetal circulation happen immediately at the time of the fetal demise. Therefore, once one fetal demise has been recognized, it is already too late to prevent the potential neurologic sequelae or subsequent fetal demise for the co-twin and conservative management is probably the best option in the absence of fetal lung maturity. Given the high risk of neurologic impairment in a surviving monochorionic co-twin, prompt delivery should be considered if fetal assessment suggests impending death of one twin.
In dichorionic twins, intrauterine fetal demise is not an indication to deliver the surviving twin unless there is a condition that may affect both fetuses–preeclampsia or intrauterine infection.
The risks and morbidity of prematurity must be considered prior to an elective delivery.
5. Prognosis and outcome
In a monochorionic pregnancy, the risk of profound hypotension following a single twin demise that results in ischemia and potential cerebral palsy in the surviving co-twin may be as high as 20%.
In addition, neurodevelopmental morbidity is also affected by the gestational age of the single intrauterine fetal demise, a recent systematic review discovered. If single demise occurred between 28 and 33 weeks of gestation, then monochorionic twins have 7-8 times higher chance of morbidity when compared to dichorionic twins at the same gestational age.
Ultrasound and magnetic resonance evaluation of the surviving co-twin can identify signs of brain injury such as white matter lesions or intracranial hemorrhage.
Single intrauterine fetal demise increases the odds of spontaneous and iatrogenic premature delivery.
The association between retention of the demised fetus and maternal disseminated intravascular coagulation is reported in the literature, though it occurs rarely. A platelet count and fibrinogen level are recommended prior to delivery.
6. What is the evidence for specific management and treatment recommendations
A recent systematic review and meta-analysis was performed evaluating 22 previously published articles evaluating the prognosis of the co-twin after single fetal demise. The authors calculated that after single intrauterine fetal demise, monochorionic co-twins were at a 15% risk for death, 34% risk for abnormal cranial imaging and a 26% risk of neurodevelopmental morbidity. In comparison, the co-twin survivor in a dichorionic pregnancy had a 3% risk of death, 16% risk for abnormal cranial imaging and only a 2% risk of neurodevelopmental morbidity. This translates into an odds ratio that is five times higher for monochorionic death after single demise when compared with dichorionic pregnancies.
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