Accuracy of trisomy 18 screening using the second-trimester triple test

Area of Science:

• Prenatal screening
• Maternal serum screening
• Genetic disorders

Background:

• Second-trimester maternal serum screening is crucial for identifying pregnancies at risk for chromosomal abnormalities.
• The triple test is a common screening tool, but its accuracy in assigning individual risk for trisomy 18 requires assessment.

Purpose of the Study:

• To evaluate the precision of calculated trisomy 18 risks provided to individual women via the second-trimester triple test.
• To validate the risk cut-off method for trisomy 18 screening.

Main Methods:

• Analysis of 382,598 women from the Ontario Maternal Serum Screening Programme (1993-2000).
• Comparison of calculated trisomy 18 risks with observed birth prevalence across 12 risk-ranked groups.
• Inclusion of 111 confirmed trisomy 18 cases.

Main Results:

• A strong agreement was observed between calculated risks and actual prevalence across all risk levels.
• High-risk pregnancies identified by the screen showed a slightly lower observed prevalence than estimated.
• The risk cut-off method demonstrated reliable risk assignment for trisomy 18.

Conclusions:

• The risk cut-off method used in the triple test accurately reflects an individual woman's risk for a term trisomy 18 syndrome pregnancy.
• This finding supports the utility of the triple test in prenatal risk assessment for trisomy 18.