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Fetal ear length measurement: a useful predictor of aneuploidy?
U Chitkara1, L Lee, J W Oehlert
1Department of Gynecology and Obstetrics, Division of Maternal-Fetal Medicine, Stanford University School of Medicine, Stanford, CA 94305-5317, USA. uchit@stanford.edu
Objective:
To determine the usefulness of short ear length (EL) measurement in the prenatal detection of fetuses with chromosomal abnormalities.
Design:
Fetal EL measurements, routine biometry and complete anatomic survey for fetal abnormalities were prospectively performed by antenatal sonography.
Subjects:
One thousand eight hundred and forty-eight patients with singleton pregnancies undergoing genetic amniocentesis in the second or third trimester.
Methods:
Complete data for EL, biometry and anatomic survey for major structural abnormalities and minor sonographic markers of chromosomal abnormality were available in 1311 fetuses. Of these, 48 (3.7%) had an abnormal karyotype and 1263 (96.3%) had a normal karyotype. Using an EL measurement of < or = 10th percentile for corresponding gestational age in normal fetuses as abnormal cut-off values, detection rates for chromosomal abnormalities by short EL were determined.
Results:
Among the 48 abnormal karyotypes, 34 were considered significant, and 11 of these 34 (32.4%) fetuses had short EL. In 14 cases, the karyotypic abnormality was considered non-significant and fetal EL was normal in all cases. Of the 34 fetuses with significant chromosomal abnormalities, six (17.6%) on antenatal sonography had no detectable abnormal findings, other than short EL. An increased biparietal diameter (BPD)/EL ratio of > or = 4.0 was also noted in fetuses with an abnormal karyotype, but the sensitivity and predictive value of increased BPD/EL ratio alone or increased BPD/EL ratio in combination with short EL was no better than the sensitivity and predictive value of short EL alone. A combination of short EL and abnormal ultrasound, however, gave a much higher positive predictive value (46%) for significant chromosomal abnormalities.
Conclusions:
Our findings suggest that in women at high risk for fetal chromosomal abnormality, a short fetal EL measurement on prenatal ultrasound, either alone or in combination with other sonographically detectable structural abnormalities, may be a useful parameter in predicting fetal aneuploidy.