Surveillance of twin pregnancy with umbilical arterial velocimetry.

A continuous-wave Doppler system and a spectrum analyzer provide the tools for the measurement of systolic-diastolic velocity wave ratios in the umbilical arteries. In twins, each umbilical cord can be studied without imaging the fetuses. Results were tabulated by taking the average difference in the ratios between each fetus and plotting these values against the neonatal weight differences. In 43 twin pregnancies, the data revealed that ratio differences between fetuses that averaged 0.4 or more was predictive of a weight difference of greater than 349 gm. The sensitivity was 73% and specificity 82%. Two cases of twin transfusion syndrome were recognized by the simultaneous presence of high- and low-resistance values.