Antenatal fetal assessment: multifetal gestation--an overview.

As prevalence of multifetal gestation has increased in the United States, antenatal surveillance of these pregnancies has gained importance. This article focuses on the assessment of twin pregnancy, since critical data are lacking for the surveillance of higher order multiple gestations. Twin pregnancies encounter risks that differ in nature, frequency, and intensity from those seen in singleton pregnancies. Most of these risks stem from subnormal or discordant fetal growth or abnormalities of placentation. Sonographic modalities play key roles in antepartum surveillance. These include fetal biometry, serial growth studies, amniotic fluid volume assessment, Doppler velocimetry of fetal-placental circulation, and biophysical profile testing. Fetal heart rate testing, specifically nonstress testing, has also been used extensively in twin surveillance. This article examines the specific application of these modalities to twin gestation and reviews the best evidence available for their support. Assessment of unique risk conditions of twin-twin transfusion, monoamniotic twinning, and intrauterine death of one twin is addressed. Based on current data, a strategic outline for assessment of twin pregnancy is presented.