First- and second-trimester Down syndrome screening: current strategies and clinical guidelines

Area of Science:

• Medical Genetics
• Prenatal Diagnosis
• Public Health

Background:

• Down syndrome (DS) is the most common chromosomal defect.
• Maternal serum screening for DS has been routine in Taiwan since 1994.
• Early screening methods relied on maternal age or history.

Purpose of the Study:

• To review Down syndrome screening options available in Taiwan.
• To evaluate the effectiveness and limitations of current screening methods.
• To provide practical information for physicians on DS screening.

Main Methods:

• Analysis of the "double test" (free beta-human chorionic gonadotropin and alpha-fetoprotein) used between 15-20 weeks gestation.
• Review of detection rates and impact on Down syndrome live birth rates.
• Comparison with first-trimester combined test and quadruple test.

Main Results:

• The double test reduced Down syndrome live births from 0.63 to 0.16 per 1,000 live births.
• The double test has a 56% detection rate, considered suboptimal.
• First-trimester combined test offers ~85% detection with a 5% false-positive rate.

Conclusions:

• The current double test is not cost-effective or sensitive enough for routine screening.
• First-trimester screening is more sensitive but logistically limited.
• The quadruple test should be considered for second-trimester screening in Taiwan.