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Is It Possible To Reduce the Incidence? What Are the Implications for Practice?
Cerebral Palsy (CP) is a chronic non-progressive symptom complex with an incidence of 1/500 births characterized by aberrant control of movement and posture. Less than 15% of cases are thought to be secondary to birth asphyxia. Additional causes of CP include low birth weight, prematurity, genetic predispositions, infection, and multiple gestations.
In the United States, the incidence of twin and higher-order multiples has been increasing since the late 1980s, and multi-fetal gestations now comprise 3% of all pregnancies. Meanwhile, twins alone are thought to account for 5-10% of all CP cases. Understanding why multiple gestations are prone to neurologic morbidity is paramount to designing and implementing prevention strategies.
Causes of neurologic morbidity in multiple gestations include preterm delivery, low birthweight, and conditions unique to twin pregnancy such as intrauterine fetal demise (IUFD) of one twin and the Twin-to-Twin Transfusion Syndrome (TTTS). In addition, monochorionic twins are susceptible to growth abnormalities including growth discordancy and intrauterine growth retardation (IUGR) which can result in fetal compromise as well as preterm delivery.
Prevention strategies for neurologic morbidity include early ultrasound diagnosis of chorionicity, targeted anatomy scans, prenatal diagnosis, and genetic counseling. Patients should be referred to specialists attuned to the problems unique to twins. Multifetal reduction should be offered to triplets and above as it has been associated with improved perinatal outcomes.
Patients should be monitored for signs and symptoms of preterm labor. Recent studies indicate that a cervical length of less than 2.5 cm has been associated with an increased risk of delivery prior to 32 weeks, and that a positive fetal fibronectin at 28 weeks has also been associated with an increased risk of preterm delivery. Nonetheless, no intervention has proven useful to prevent preterm labor. Both prophylactic cerclage and prophylactic tocolysis have not improved outcomes in patients with multiple gestations. Due to the risk of adverse maternal sequelae such as fluid overload, tocolysis should be utilized only in cases of documented preterm labor. In any situation where delivery is thought to occur between 24 and 34 weeks, it is recommended that antenatal steroids be administered.
Frequent ultrasounds are suggested to identify growth abnormalities in both dichorionic and monochorionic twins. Once weight discordancy or IUGR has been diagnosed, antepartum surveillance should be initiated. IUFD in one monochorionic twin is challenging since the exact pathophysiology of the neurologic morbidity associated with this occurrence is unknown, making it difficult to prevent. Monochorionic twins at risk for IUFD require intense fetal monitoring. Early delivery should be considered if IUFD is thought to be imminent.
Patients with mulitifetal pregnancies discordant for structural and/or chromosomal abnormalities should be counseled about their options including expectant management or depending upon the gestational age at diagnoses and the severity of the anomaly either termination or selective termination. New technologies including radio-ablative therapy are being tested as safe options for selective termination in monochorionic pregnancies. The management of Acardia remains controversial. The goal is maximizing the normal twin’s outcome. Expectant management with serial ultrasound is reasonable in many cases. Several percutaneous procedures have been described and are still experimental for cases of Acardia with poor prognostic indicators. At this point, the optimal management for TTTS is unknown. A randomized prospective NIH trial is currently ongoing to determine if serial amnioreduction versus laser ablation improves outcomes.
In summary, multiple gestations are increasing and these fetuses have significant risk for neurologic morbidity. Multiple management strategies, including early and frequent ultrasounds to determine chorionicity, to diagnosis abnormalities, and to follow growth, are needed. Likewise, it is recommended that women be counseled about the signs and symptoms of preterm labor. Pathophysiologic states unique to twins such as anomaly discordancy, IUFD of one twin, monoamnionicty, Acardia, and TTTS should be managed by specialists knowledgeable about these disease processes.