Fetal internal carotid artery flow velocity time waveforms in twin pregnancies.

The fetal internal carotid artery and umbilical artery flow velocity time waveforms were studied in 17 consecutive twin pregnancies. The pulsatility index was calculated for each fetus in each artery as an index of vascular resistance. All studies were done within 14 days before delivery. In 8 pregnancies both fetuses were of birthweight appropriate for gestational age; whereas, in 9 patients one or both of the infants were small for gestational age (SGA). From ultrasound criteria and Doppler studies of the umbilical and fetal internal carotid arteries, decreased fetal internal carotid artery pulsatility index (cut off value less than or equal to 1.2) was found to be the best predictor of SGA (sensitivity 83%, specificity 95%, positive predictive value 91%, negative predictive value 91%).