PT/NBL ratio assessment at mid-trimester in prenatal screening for Down syndrome in a Chinese population.
OBJECTIVE
To investigate the ratio of prenasal thickness (PT) to nasal bone length (NBL) in normal and trisomy 21 fetuses in the second and third trimester in Chinese population.


METHODS
The NBL and PT were measured blindly by using 3D volumes in 143 normal fetuses and 31 trisomy 21 fetuses.


RESULTS
The mean PT (r = 0.83, p = 0.004) and NBL (r = 0.87, p = 0.0062) both increased with the gestation age, while the PT/NBL ratio (r = 0.12, p > 0.10) remained stable. There was significant difference between normal and trisomy 21 fetuses (p < 0.001). If we took the 95th of the normal fetuses as the cut-off value, the detection rate was only 46%. By using ROC curve to evaluate the screening value of PT/NBL ratio, the area under receiver operating characteristic (ROC) curve was 0.88 (95% confidence interval 0.81 to 0.94, p < 0.0001).


CONCLUSIONS
In Chinese population, the PT/NBL ratio is not a very strong ultrasound marker to predict trisomy 21 fetuses. However, it can be used as an ultrasound marker for Down syndrome screening during the second and third trimester of pregnancy.
Prenatal Diagnostic Center, Guangzhou Maternal and Neonatal Hospital , Guangzhou, Guangdong , China.
Xin
X
Yang
Li
L
Zhen
Min
M
Pan
Jin
J
Han
Dongzhi
D
Li
Can
C
Liao
D044466:Asian People; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000208:ethnology; D005260:Female; D005333:Fetus / Q000033:anatomy & histology; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D009295:Nasal Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D009666:Nose / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D009929:Organ Size; D011237:Predictive Value of Tests; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D016216:Ultrasonography, Prenatal / Q000379:methods*
Chinese population; nasal bone length; prenasal thickness; screening; trisomy 21