The length of a fetus's ear may be an indicator of aneuploidy, especially when other sonographically detectable structural abnormalities are present.



(1) vertical length of the ear in mm

(2) gestational age in weeks

(3) 10th percentile for ear length for a gestational age and ethnic group (approximately 1.3 standard deviations below the mean)

(4) biparietal diameter in mm


biparietal diameter to ear length ratio =

= (biparietal diameter in mm) / (ear length in mm)


Criteria for aneuploidy:

(1) length of the ear <=10th percentile

(2) biparietal diameter to ear length ratio >= 4


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