Ultrasonographic prediction of homozygous alpha0-thalassemia using placental thickness, fetal cardiothoracic ratio and middle cerebral artery Doppler: alone or in combination?
OBJECTIVE
To compare the predictive values of three ultrasonographic parameters: placental thickness (PT), fetal cardiothoracic ratio (CTR) and middle cerebral artery peak systolic velocity (MCA-PSV), alone or in combination, in pregnancies affected by homozygous alpha(0)-thalassemia at 12-20 weeks' gestation.


METHODS
Pregnant women at risk of carrying a fetus affected by homozygous alpha(0)-thalassemia were studied from 1995 to 2006 using serial ultrasonography at 12-15 weeks, 16-20 weeks and 30 weeks' gestation. We measured CTR and PT from 1995, and MCA-PSV as well from 1997. An invasive prenatal test was offered if cardiomegaly with or without placentomegaly was detected but the MCA-PSV results were used only retrospectively for analysis.


RESULTS
Of a total of 777 at-risk fetuses studied, 138 (17.8%) were affected by homozygous alpha(0)-thalassemia. At 12-15 weeks' gestation, 598 ultrasound examinations were performed. CTR was better than both PT and MCA-PSV in the prediction of affected pregnancies. The highest sensitivity (98.3%) was achieved by the combination of CTR and/or MCA-PSV at a false-positive rate of 15.8%. At 16-20 weeks' gestation, 410 ultrasound examinations were performed, 121 of which were at the patient's first visit and 289 of which were at a follow-up visit. Both CTR and MCA-PSV predicted the affected pregnancies equally well. The sensitivity of CTR was 100.0%, but the false-positive rate was 5.2%. In contrast, the false-positive rate of MCA-PSV alone was 1.4% and that of the combination of CTR and MCA-PSV was 0%, although their sensitivities were less than 65%.


CONCLUSIONS
The data suggest that adding MCA-PSV to CTR in the prediction of homozygous alpha(0)-thalassemia can increase the sensitivity at 12-15 weeks and decrease the false-positive rate at 16-20 weeks' gestation.
Leung
K Y
KY
Department of Obstetrics & Gynaecology, The University of Hong Kong, Queen Mary Hospital, Hong Kong, Republic of China. leungky1@ha.org.hk
Cheong
K B
KB
Lee
C P
CP
Chan
V
V
Lam
Y H
YH
Tang
M
M
D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000503:physiopathology; D001783:Blood Flow Velocity / Q000502:physiology; D006332:Cardiomegaly / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006720:Homozygote; D006801:Humans; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging* / Q000503:physiopathology; D010920:Placenta / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011237:Predictive Value of Tests; D011247:Pregnancy; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods; D017085:alpha-Thalassemia / Q000000981:diagnostic imaging* / Q000235:genetics / Q000503:physiopathology