Nasal-bone length in euploid fetuses at 16-24 weeks' gestation by three-dimensional ultrasound.
OBJECTIVE
To establish a normal range of nasal-bone length at 16-24 weeks' gestation by the use of three-dimensional (3D) ultrasound and to investigate the effect of deviations from the exact mid-sagittal plane on the measurement of nasal-bone length.


METHODS
We acquired 3D volumes of the fetal profile from 135 normal fetuses at 16-24 weeks' gestation. The multiplanar mode was used to obtain the exact mid-sagittal plane and to produce parasagittal and oblique views of the fetal face. Nasal-bone length was measured in each plane and the sonographic landmarks of each profile view were examined.


RESULTS
Nasal-bone length increased with gestational age from a mean of 4.1 mm at 16 weeks to 7.1 mm at 24 weeks. There was a tendency to underestimate nasal-bone length when the measurements were taken in parasagittal planes and to overestimate the measurements when they were taken in oblique views, compared to the exact mid-sagittal plane. The mean difference in nasal-bone length from the one in the mid-sagittal plane was 0.42 and 0.63 mm for parasagittal measurements at 1 and 2 mm, respectively, from the midline, -0.08 and -0.51 mm for oblique measurements at 10 degrees and 20 degrees rotation along the z-axis and -0.69 mm for rotation of 20 degrees along the z-axis and 10 degrees along the y-axis. The vomeral bone was the only sonographic landmark defining the exact mid-sagittal plane of the face that was not visible in the parasagittal and oblique planes.


CONCLUSIONS
Parasagittal and oblique scanning planes may produce different degrees of under- or over-estimation of nasal-bone length compared to measurements systematically taken in the exact mid-sagittal plane. Inclusion of the vomeral bone in the definition of the exact mid-sagittal plane of the face could improve the reproducibility of measurements of nasal-bone length.
Persico
N
N
Department of Fetal Medicine, King's College Hospital, London, UK.
Molina
F
F
Borenstein
M
M
Azumendi
G
G
Nicolaides
K H
KH
D000293:Adolescent; D000328:Adult; D005145:Face / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000196:embryology; D005260:Female; D005865:Gestational Age; D006801:Humans; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D009295:Nasal Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000196:embryology; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods*; D055815:Young Adult