First-Trimester Combined Test Screening for Down Syndrome: Results of a Series with 5,036 Cases

Objective: To assess the sensitivity of a first-trimester combined screening test for fetal chromosomal abnormalities. Materials and Methods: From April 1999 to December 2002, 5,036 unselected women with singleton pregnancies underwent a first-trimester combined test (nuchal translucency thickness, pregnancy-associated plasma protein-A, and freeβ-human chorionic gonadotropin) screening for Down syndrome. They included 298 (5.9%) women aged 35 years or older and 4,738 (94.1%) women aged below 3S years. A positive result was defined as an estimated Down syndrome risk of greater than 1/270. Results: Twenty-five (0.50%) chromosomal abnormalities were identified, with a false-positive rate of 7.1 % (333j4,717) in women younger than 3S years and a false-positive rate of17.3% (S1j294) in women of advanced maternal age. The 25 chromosomal abnormalities included trisomy 21 in six fetuses, trisomy 18 and Turner’s syndrome in four fetuses each, Klinefelter’s syndrome, a marker chromosome and pseudohermaphroditism in one fetus each, and structural rearrangements in eight, including four with balanced translocations. One fetus with trisomy 18 was not discovered at screening, but a fetal ventricular septal defect was found on ultrasound at 30 weeks’ gestation. The detection rate for fetal chromosomal abnormalities was 95.2% (20/21). If a cutoff of 1 in 200 was used, the false-positive rate would be 5.6% with the same detection rate, whereas the test still yielded a detection rate of 90.5% (19/21 ) with a 5% false-positive rate. I n 83.3% of cases with trisomy 21 and 5.7% of normal pregnancies, fetal nuchal translucency thickness measurement was above the 95th percentile, whereas in 0.7% of the study population and in 24% of those with fetal chromosomal abnormalities, the fetal nuchal translucency thickness was at least 3 mm. Conclusions: Our results indicate that the first-trimester combined test for Down syndrome is effective in identifying fetal chromosomal abnormalities. Moreover, the measurement of fetal nuchal translucency thickness at 10 to 13 weeks of gestation enables early detection of major fetal structural anomalies. [Taiwanese J Obstet GynecoI2004; 43(2):72-76]

並列關鍵字

chromosomal abnormaiity ； Down syndrome screening ； human chorionic gonadotropin ； nuchal translucency ； pregnancy-associated plasma protein-A

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