Differences between Twin Umbilical Coiling Indices Correlate to Differences in Twin Weight and Doppler Indices

> Objective: The aim of our study was to evaluate sonographic and Doppler detectable differences in umbilical coiling index and fetoplacental circulation of discordant twins. Study Design: Doppler blood flow studies in 13 pairs of concordant and 20 pairs of discordant twins were performed from umbilical artery, middle cerebral artery, inferior vena cava, and ductus venosus. Flow studies were compared and correlated with the antenatal sonographic coiling index and the actual umbilical cord length, number of vascular helices, and birth weight. All studies were performed within 72 h before delivery. Pulsatility index (PI) values were calculated for the arteries and preload index (PLI) values for the veins. The umbilical coiling index (CI) was calculated using sonographic longitudinal views of cord vessels from several segments antenatally and by dividing the total number of helices by cord length (cm) postnatally. Discordancy was defined as a more than 20% intrapair actual birth weight difference. For all these index values the intertwin differences (Delta values) were calculated by subtracting the values obtained in the larger twin with those of the smaller twin. Results: The mean +/- SD intertwin difference in umbilical coiling index was 27.4 +/- 10.5% in the antepartum period and 28.9 +/- 10.0% after birth. Regression analysis showed a significant linear trend (r = 0.77, P < 0.001) between intertwin birth weight difference (DeltaBW) and intertwin coiling index difference (DeltaCI). A good correlation was found between DeltaCI and DeltaPLI in the ductus venosus (r = 0.63, P < 0.05), DeltaPLI in the inferior vena cava (r = 0.51, P < 0.005), and DeltaPI in the middle cerebral artery (r = 0.44, P < 0.05). Conclusions: Intertwin difference in antepartum umbilical coiling index can be determined by ultrasound and correlates well with: 1) the actual difference in coiling indices at birth, 2) the intertwin birth weight difference and 3) the intertwin Doppler flow characteristics in the fetal cerebral and venous circulation.