Comparison and integration of first trimester fetal nuchal translucency and second trimester maternal serum screening for fetal Down syndrome.
BACKGROUND
It is uncertain whether first trimester nuchal translucency (NT) is more effective than the well-established second trimester serum screening for fetal Down syndrome or whether their combination works best. We report data from a large multicentre non-interventional trial in which all subjects underwent both first and second trimester screening.


METHODS
All women who attended the obstetric clinic before 15 weeks' gestation were recruited. An ultrasound examination was performed at 10 to 14 weeks to measure the NT. The nuchal measurements were not acted upon unless the fetus showed gross features of hydrops fetalis. All women had serum alpha-fetoprotein (AFP) and human chorionic gonadotrophin (hCG) assay at 15 to 20 weeks. The Down syndrome risk assigned by serum screening was disclosed and amniocentesis was offered if this assigned risk was >or=1:250 or if the women were 35 years and older. The efficacy of different combinations of screening markers was compared.


RESULTS
Between January 1997 and August 2000, 17 590 women were recruited (19% >or=35 years old). After excluding subjects who miscarried, defaulted the serum test and other reasons, 16 237 pregnancies were analysed. Of these, 35 pregnancies were affected by Down syndrome (2.2 cases per 1000 pregnancies). At a false-positive rate of 5%, the detection rate of Down syndrome by NT alone, NT and age, serum hCG, AFP and age, and NT, hCG, AFP and age were 61%, 69%, 73% and 86%, respectively.


CONCLUSIONS
Integration of NT and second trimester serum AFP and hCG assay yielded the best screening efficacy for Down syndrome.
Lam
Yung Hang
YH
Department of Obstetrics and Gynaecology, The University of Hong Kong, Tsan Yuk Hospital, Hong Kong, China. yhlamobgyn@yahoo.com.hk
Lee
Chin Peng
CP
Sin
Sai Yuen
SY
Tang
Rebecca
R
Wong
Hong Soo
HS
Wong
Sai Fun
SF
Fong
Danial Yee Tak
DY
Tang
Mary Hoi Yin
MH
Woo
Hennie Hai Nin
HH
D000649:Amniocentesis; D015415:Biomarkers / Q000097:blood*; D006063:Chorionic Gonadotropin / Q000097:blood; D004314:Down Syndrome / Q000097:blood / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005189:False Positive Reactions; D005865:Gestational Age; D015160:Hydrops Fetalis / Q000000981:diagnostic imaging; D008423:Maternal Age; D009333:Neck / Q000000981:diagnostic imaging* / Q000196:embryology*; D018566:Pregnancy, High-Risk; D011296:Prenatal Diagnosis; D012372:ROC Curve; D012307:Risk Factors; D016216:Ultrasonography, Prenatal; D000509:alpha-Fetoproteins / Q000032:analysis
D015415:Biomarkers; D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins