Congenital heart defects in twin gestations.

As ultrasound technology advances, diagnosis of fetal malformations, particularly congenital heart defects (CHD) is becoming standard practice. Currently, a key element of obstetrical care is the use of ultrasound to diagnose chorionicity in multiple gestations. Given the difference in incidence and types of complications between dichorionic and monochorionic pregnancies, early diagnosis of chorionicity is critical to determine the type of care and counseling a patient receives throughout the pregnancy. Early diagnosis of chorionicity allows investigators to more accurately determine the risk of CHD in monochorionic pregnancies. It has been long known that twin gestations incur a higher risk of congenital malformations, including CHD. However, it was not until recently that the incidence could be determined according to chorionicity. Previous studies looking at risk of malformations including CHD used the like-sex technique as a proxy for chorionicity, thereby overestimating the prevalence of monochorionic twins because roughly two-thirds of all twin gestations (including dichorionic) are the same sex. The rate of multiple gestations is increasing in the developed world. Assisted reproductive technology (ART) is partly responsible for the increased incidence of multiples. While many of the ART conceived pregnancies are dichorionic multiples, there is evidence that ART increases the risk of monochorionic multiple gestations. Presently, it is not technically feasible, nor practical, to screen all pregnancies with fetal echocardiography. Thus, many perinatal ultrasound centers screen women for risk factors that place them at higher risk for having a fetus with CHD. This higher risk' group then receives a fetal echocardiogram. The available literature regarding risk of CHD in monochorionic multiple gestations strongly points to a significant increase over the general population risk of 0.5-0.8%. Fetal echocardiography is technically feasible in twin pregnancies and increasingly available. Monochorionic multiple gestations should be screened with fetal echocardiography.