Progression of nonimmune hydrops in a fetus with Noonan syndrome.

Presented is a case of nonimmune hydrops caused by Noonan syndrome. This autosomal dominant disorder, with an incidence of 1 in 1000 births, is manifested by trunk and limb edema, lymphatic abnormalities, webbed neck, short stature, and cardiac and genital anomalies. In this case the initial presentation was polyhydramnios at 31 weeks' gestation, followed in 1 week by pleural effusions and a week later by skin edema. An 18-week ultrasound had been normal. Because of variable expressivity, only the most severe cases of the disease are usually diagnosed. Thus, the incidence may be higher than 1 in 1000, and Noonan syndrome may be underdiagnosed as a cause of nonimmune hydrops. Since lymphedema in this syndrome may regress spontaneously, conservative obstetric management is preferable unless the fetus develops distress.