Radiology, Vol 196, 541-545, Copyright © 1995 by Radiological Society of North America
Homozygous achondroplasia: US distinction between homozygous, heterozygous, and unaffected fetuses in the second trimester
MD Patel and RA Filly
Department of Radiology, University of California 94110, USA.
PURPOSE: To determine if and at what gestational age prenatal
ultrasonography (US) enables distinction between homozygous, heterozygous,
and unaffected fetuses when both parents have heterozygous achondroplasia.
MATERIALS AND METHODS: Serial US scans of 15 fetuses at 25% risk of
homozygous achondroplasia were reviewed retrospectively. Femoral growth
curves were established and compared with published standards to determine
the gestational age, calculated according to biparietal diameter (BPD), at
which femoral length crossed below the 3rd percentile. The presence and
severity of achondroplasia were determined clinically after birth. RESULTS:
Femoral length crossed the 3rd percentile at 14.0-16.5 weeks BPD age (mean,
15.6 weeks) in the four homozygous fetuses and at 18.2-26.2 weeks BPD age
(mean, 21.5 weeks) in the eight heterozygous fetuses. In the three
unaffected fetuses, femoral length did not cross percentiles as gestational
age increased. CONCLUSION: Establishment of a femoral growth curve in the
second trimester with serial US scans enables prenatal distinction between
homozygous, heterozygous, and unaffected fetuses when both parents have
heterozygous achondroplasia.
