Objective: To evaluate the role of the early second-trimester Doppler velocimetric studies of the umbilical coiling index and umbilical cord cross-sectional area as tests for the prediction of small-for-gestational age infants.
Methods: Doppler blood flow studies in 147 singleton pregnancies at risk for delivery of a small-for-gestational-age neonate were performed at 15 +/- 1 (SD) weeks' gestation from the uterine artery, umbilical artery, middle cerebral artery, inferior vena cava, and ductus venosus. Pulsatility index values were calculated for the arteries, and preload index values and systolic-atrial contraction ratios were calculated for the veins. The sonographic cross-sectional area of the umbilical cord was measured in a plane adjacent to the insertion into the fetal abdomen. The umbilical coiling index was calculated by using sonographic longitudinal views of cord vessels from several segments antenatally and by dividing the total number of helices by cord length (centimeters) postnatally. Small-for-gestational-age neonates were identified when the birth weight was below the 10th percentile for gestational age.
Results: Among 147 pregnancies studied, 124 fulfilled the study criteria. Thirty-nine of the neonates were small for gestational age at birth (31.5%). The mean +/- SD gestational age at delivery of the appropriate-for-gestational-age neonates was 39.7 +/- 1.28 weeks, and that of the small-for-gestational-age neonates was 36.4 +/- 2.9 weeks (range, 28-40 weeks). The best single predictor of a small-for-gestational-age infant was the coiling index, with sensitivity of 79%, specificity of 86%, a positive predictive value of 72%, and a negative predictive value of 90%.
Conclusions: The umbilical coiling index measured in the second trimester is useful in predicting the birth of a small-for-gestational-age infant and may serve as a marker for subsequent growth restriction.