Comparison between two- and three-dimensional ultrasound measurements of nuchal translucency.
OBJECTIVE
Fetal nuchal translucency measurement has been introduced as a screening test for the calculation of risk of chromosomal abnormalities. The purpose of this study was to investigate: (1) the feasibility of obtaining nuchal translucency measurements using three-dimensional ultrasound; (2) whether three-dimensional ultrasound could improve and facilitate the required repeated measurements of nuchal translucency; (3) the correlation between two- and three-dimensional nuchal translucency measurement values.


METHODS
Between September 1999 and May 2000, in a prospective cohort study, 229 unselected pregnant women with a mean age of 34.6 (range, 20-46) years were examined. The mean fetal crown-rump length was 64.3 (range, 45-84) mm. Nuchal translucency thickness was measured first by two- and then by three-dimensional ultrasound in two planes (three-dimensional mid-sagittal and three-dimensional transverse). An attempt was made to repeat each nuchal translucency measurement three times (totalling nine measurements per patient) and the means of the two- and three-dimensional measurements were compared. The majority (95%) of the measurements were made transabdominally and 5% were made transvaginally. The time limit for each examination was 20 min.


RESULTS
With the two-dimensional method, nuchal translucency could be measured in 96.8% of cases. Of these, three measurements could be obtained in 51.7%, two in 23.2% and only one in 25.1%. The three-dimensional examination was successful in 98.6% of cases. Of these, three measurements could be obtained in 60%, two in 22.8% and one in 17.2%. Transvaginally, all examinations were successful. The main reason for the failure of two-dimensional ultrasound was the fetal position, which in some cases precluded the distinction between fetal skin and amnion or the uterine wall. Using two-dimensional ultrasound, 6.3% of the cases of measurement failure were due to an inability to differentiate clearly between fetal skin and amnion, whilst the equivalent value for the three-dimensional method was only 3.3%. For the three-dimensional technique, fetal movement was the main reason for failure. The mean time for both methods was similar (9 min and 10 min for two- and three-dimensional ultrasound, respectively) and the correlation between the measurements obtained by the two- and three-dimensional techniques was very high (r = 0.97).


CONCLUSIONS
The number of fetuses in which nuchal translucency could be measured tended to be higher with three-dimensional ultrasound, although the difference was not statistically significant. The possibility of rotating a stored volume and inspecting it in three orthogonal planes makes three-dimensional ultrasound a useful tool for nuchal translucency measurements, especially in doubtful cases.
Clementschitsch
G
G
Department of Obstetrics and Gynecology, Prenatal Diagnosis and Therapy Unit, St. Johannsspital Salzburg, Salzburg, Austria.
Hasenöhrl
G
G
Schaffer
H
H
Steiner
H
H
D000328:Adult; D025063:Chromosome Disorders / Q000000981:diagnostic imaging; D004487:Edema / Q000000981:diagnostic imaging; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011446:Prospective Studies; D012307:Risk Factors; D018615:Ultrasonography, Doppler, Color; D016216:Ultrasonography, Prenatal