Objectives: We aimed to test the predictive value of antenatal umbilical coiling index (aUCI) among a prospectively recruited cohort of antenatal women. Methods: Women with singleton pregnancies were recruited at their second-trimester scan. Images of the umbilical cord were used to calculate the aUCI. Pregnancy and birth outcomes were recorded and statistical associations between aUCI and small for gestational age (SGA) using international standard birth weight centiles and preterm birth were investigated (n = 430). Results: aUCI results were consistent with the literature and showed good reproducibility between observers. Abnormal aUCI was not associated with SGA, but there was a statistical association with preterm birth (odds ratio 3.3 (95% confidence interval 1.4–7.7, P = 0.003). The sensitivity, specificity, and positive and negative predictive values for preterm birth were 47.6%, 76.9%, 9.6%, and 96.6%, respectively. Conclusions: The coiling index is unlikely to be useful in clinical practice as a screening tool for preterm birth owing to limited predictive value. We exclude a statistically or clinically significant association between abnormal coiling and SGA.