First-trimester screening for trisomies 21 and 18.

Area of Science:

• Prenatal Diagnostics
• Maternal-Fetal Medicine
• Genetics

Background:

• Routine aneuploid pregnancy screening occurs after 15 weeks gestation with 65% sensitivity and 5% false positive rate.
• First-trimester aneuploidy screening markers exist but lack comprehensive clinical evaluation.

Purpose of the Study:

• To evaluate the clinical effectiveness of first-trimester screening for trisomies 21 and 18.
• To assess the sensitivity and false positive rates of this combined screening approach.

Main Methods:

• A multicenter study screened 8514 singleton pregnancies between 74-97 days gestation.
• Screening utilized maternal age, free beta human chorionic gonadotropin, pregnancy-associated plasma protein A, and fetal nuchal translucency.
• Positive screening defined as risk >= 1:270 for trisomy 21 and >= 1:150 for trisomy 18.

Main Results:

• The screening identified 85.2% of Down's syndrome cases with a 9.4% false positive rate.
• At a 5% false positive rate, Down's syndrome detection was 78.7%.
• Screening identified 90.9% of trisomy 18 cases with a 2% false positive rate.

Conclusions:

• First-trimester screening for trisomies 21 and 18 demonstrates good sensitivity.
• The combination of maternal age, biochemical markers, and nuchal translucency offers an acceptable false positive rate.
• This approach provides effective early detection of common aneuploidies.