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Volume 62, Number 4, 2010
Specificity of Hypocoiled Umbilical Cord in Prediction of Fetal Trisomy 21 in the Second Trimester
Nisarat Phithakwatchara, M.D.,Chayawat Phatihattakorn, M.D.
Department of Obstetrics and Gynecology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.

Abstract
Objective: To assess the sonographic morphology of umbilical cord coiling in chromosomally normal fetuses and estimate the specificity of hypocoiled appearance as a marker for fetal trisomy 21 in the second trimester.
Methods: 555 singleton pregnancies undergoing amniocentesis for fetal karyotype were scanned at 17-22 weeks’ gestation. The umbilical cord was evaluated in a longitudinal section using 2D with color Doppler sonography. The cross-sectional data of umbilical coiling index (UCI), defined as the reciprocal of the distance between umbilical coils, were analyzed to establish the normal range according to the gestational age. A UCI less than the 5th percentile was the cut-off value for hypocolied umbilical cord. The specificity of hypocolied umbilical cord to predict fetal trisomy 21 was calculated.
Results: As a result of amniocentesis, there were 527 chromosomally normal fetuses and 9 trisomy 21 fetuses. There was no significant difference in maternal characteristics between these two groups. In trisomy 21 fetuses, there was a higher proportion of fetal anomaly indicating for fetal karyotype (22.2% VS 0.6%, p = 0.003). The regression equation of UCI (cm-1, y) on gestational age (weeks, x) was y = 1.205 - 0.033x. The hypocoiled umbilical cord was characterized in 2/9 (22.2%) fetuses with trisomy 21 and in 22/527 (4.2%) chromosomally normal fetuses (p = 0.01), with specificity of 95.83%.
Conclusion: The coiling pattern of umbilical cord visualized by sonography has a potential value in second-trimester screening for fetal trisomy 21. Nevertheless, further studies of this model in a larger cohort would provide more information in sensitivity and predictive values.

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