[Clinical significance of ultrasonographic screening for Down syndrome in the second trimester].

OBJECTIVE

This study was undertaken to evaluate the clinical significance of ultrasonographic screening for the detection of Down syndrome in the second trimester of pregnancy of Japanese women.

MATERIALS AND METHODS

BPD (biparietal diameter), FL (femur length), BPD/FL ratio and M/E FL (measured/expected femur length) ratio were measured in 734 normal second-trimester fetuses and 13 consecutive Down syndrome fetuses undergoing genetic amniocentesis mainly for advanced maternal age.

RESULTS

Two fetuses with Down syndrome had small BPD, three fetuses had a short femur length, four fetuses had a high BPD/FL ratio and four fetuses had a low M/E FL ratio. A cutoff value of 1.5SD below the mean value for the normal populations for BPD and FL, that of above 1.5SD for BPD/FL ratio, and that of 0.91 or less for M/E FL ratio yielded a sensitivity of 15.4, 23.1, 30.8 and 30.8% and false positive rates of 2.7, 6.0, 5.7 and 11.4%, respectively.

CONCLUSION

The ultrasonographic measurements of femur length for the screening of Down syndrome in the Japanese population revealed the low discriminative ability reported in recent studies conducted in Western countries. Further investigation would be necessary to apply it as the routine screening method for Down syndrome in clinical practice.