A model for second-trimester Down syndrome sonographic screening based on facial landmarks and digit length measurement.
OBJECTIVE
To determine whether Down syndrome can be detected by combining measurements of fetal nasal bone (NB) length, prenasal thickness (PT) and digits 2 and 3 of the hand.


METHODS
Two hundred and fifty-four normal and 25 Down-syndrome fetuses were scanned between 15 and 33 weeks' gestation. Physicians performing the scans were not blinded to the fetal karyotype. Both PT and NB were measured in a mid-sagittal plane. For PT measurement calipers were placed between the frontonasal angle and the outer skin edge. Digits 2 and 3 of one hand were also measured. The results (except for PT/NB ratio) were expressed in multiples of the normal gestation-specific median (MoM). A logistic regression model was used to estimate the odds of the fetus having Down syndrome given different combinations of NB, PT, PT/NB ratio, and digits 2 and 3 measurements. The odds were used to calculate the risk of Down syndrome for each pregnant woman from her age and measurements.


RESULTS
The median PT MoM for unaffected fetuses and Down-syndrome fetuses was 1.12 vs. 1.35 (P < 0.0001). The median NB MoM for unaffected and Down-syndrome fetuses was 1.03 vs. 0.81 (P < 0.001) and the PT/NB ratio MoM for unaffected and Down-syndrome fetuses was 0.63 vs. 0.96 (P < 0.001). The respective median MoM values for digits 2 and 3 of the Down-syndrome fetuses were significantly smaller (0.81 vs. 0.93 and 0.89 vs. 0.95, respectively, P = 0.003). Only the PT/NB ratio and digit 2 were finally included in the logistic regression equation. Using a 1 in 200 risk cut-off, the observed sensitivity and false-positive rate were 76% and 6.7%, respectively.


CONCLUSIONS
Combining the PT/NB ratio and digit 2 measurements yielded a promising screening detection rate. Confirmation of our findings in a prospective study is needed before the method can be used clinically.
Maymon
R
R
Department of Obstetrics and Gynecology, Assaf Harofe Medical Center, Affiliated to The Sackler Faculty of Medicine, Tel Aviv University, Zerifin, Israel. intposgr@post.tau.ac.il
Ushakov
F
F
Waisman
D
D
Cuckle
H
H
Tovbin
Y
Y
Herman
A
A
D000328:Adult; D001699:Biometry; D003430:Cross-Sectional Studies; D004314:Down Syndrome / Q000000981:diagnostic imaging*; D005260:Female; D005385:Fingers / Q000000981:diagnostic imaging / Q000196:embryology*; D005865:Gestational Age; D006801:Humans; D009295:Nasal Bone / Q000000981:diagnostic imaging / Q000196:embryology*; D015588:Observer Variation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011446:Prospective Studies; D014463:Ultrasonography