Ear length: A potential sonographic marker for Down syndrome

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Abstract
The purpose of this study was to determine if antenatal sonographic determination of fetal ear length is a useful screening method for identification of fetuses with Down syndrome. Ear length measurements were recorded in 418 fetuses undergoing ultrasound scanning between 20 and 28 weeks of gestation. Four trisomy 21 and six trisomy 18 fetuses were identified by karyotyping. The relationship between ear length and gestational age in the normal population was determined by linear regression analysis: expected ear length = -6.000 + 1.075 gestational age. The ability of measured-to-expected ear length cut-off ratios to discriminate between affected and non-affected fetuses was assessed. The mean ear length and measured-to-expected ear length ratios were significantly lower in the affected group as compared to the normal one. A measured-to-expected ear length ratio of less than 0.8 was 75.0% sensitive and 98.8% specific in detecting Down syndrome fetuses, and resulted in an 8.5% positive predictive value in the general population. This preliminary study suggests that antenatal ear length measurements might be a promising sonographic screening method for the detection of Down syndrome in the second trimester of pregnancy.