Twin pregnancies, especially those in which the twins share one placenta but have separate amnion sacs (referred to monochorionic, diamniotic or Mo-di twins), are at risk for a number of complications. Most notable of these is twin-twin transfusion syndrome. This condition can result in fetal morbidity or intrauterine fetal demise but is also amenable to surgical intervention. Severe discordance in amniotic fluid volumes between each twin is the prenatal finding that highlights this diagnosis. Selective laser photocoagulation has greatly improved the survival of twins with this condition. With a posteriorly located placenta, laser ablation of the abnormal placenta vascular communications can be achieved with local anesthesia and maternal sedation. Anterior placenta location may present a challenge for uterine access that may require modification of the anesthetic technique.

The chapter opens with observations on the normal fetal heart and proceeds to a discussion of fetal hydrops and its associated cardiac causes. There follows a treatment of the syndromes associated with congenital heart disease in the fetus. Common congenital heart defects as they appear in the fetus are illustrated. Fetal cardiomyopathy, myocarditis and arrhythmia all have separate discussions. The chapter closes with a series of discussions on the pathology of twins as it affects the heart: twin–twin transfusion syndrome, conjoined twins and acardiac twins.