Ultrasound evaluation of umbilical coiling index in second trimester of gestation and its association with small for gestational age status at birth

Introduction: The degree of coiling of the umbilical cord, referred to as umbilical coiling index, has been shown to have an effect on perinatal adverse outcomes such as small for gestational age neonates, interventional delivery, meconium staining, low fetal pH and low Apgar score. This study proposes that the antenatal umbilical coiling index performed in the second trimester of pregnancy has a correlation with the gestation-specific birth weight and can therefore be used as a marker to predict small for gestational age neonates. Objective: To determine the association between antenatal umbilical coiling index (aUCI) in the second trimester and small for gestational age neonates. Methods: A prospective cohort study was carried out on 421 gravid women between 18 and 24 weeks gestation who presented to the Radiology department at the Aga Khan University Hospital, Nairobi for obstetric ultrasonography. The antenatal umbilical coiling index was calculated and the study participants followed up at delivery where the birth weight was recorded and grouped into the respective centiles to diagnose small for gestational age neonates. Results: The odds ratio of the association between abnormal coiling index vs. small for gestational age at birth was 0.8 (95% CI:0.37– 1.72, p 0.562). In the analyses of factors associated with aUCI, it was found that preterm delivery was associated with abnormal coiling(Odds ratio 2.9, 95% CI: 1.0 – 8.2, p 0.037). The interobserver variability in the calculation of the antenatal umbilical coiling index according to Kappa statistics was 0.95 and according to the AC1 statistic was 0.91. Discussion: Previous studies have shown a wide variation in the association between coiling and adverse perinatal outcomes, especially small for gestational age at birth. The current study, however, found no association between abnormal coiling and small for gestational status at birth. As in other studies, preterm deliveries was associated with abnormally coiling, which has been proposed to be due to an adaptive fetal haemodynamic response. The almost perfect inter-observer variability observed is reproduced in other studies and demonstrates that the measurement of aUCI is highly reproducible. Conclusion/Recommendation: There is insufficient evidence to support an association between antenatal umbilical coiling index and small for gestational age (SGA) status at birth and therefore its proposed use to potentially predict SGA status at birth is not plausible