Where have all the trisomies gone?

Area of Science:

• Obstetrics and Gynecology
• Medical Genetics
• Fetal Medicine

Background:

• Prenatal screening for aneuploidy is essential for patient counseling and policy development.
• Sequential screening (serum and ultrasound) is a common primary test for aneuploidy detection.
• Cell-free DNA (cfDNA) screening is a newer, noninvasive secondary option for screen-positive cases.

Discussion:

• Both sequential and cfDNA screening are noninvasive and detect common aneuploidies.
• cfDNA screening identifies more common chromosomal abnormalities like trisomy 21 and sex trisomies.
• Sequential screening can detect other aneuploidies (e.g., triploidy) and abnormalities linked to fetal structural defects.

Key Insights:

• A direct comparison of sequential and cfDNA screening performance is critical.
• The proportion and severity of identified chromosomal abnormalities are key comparative measures.
• Accurate reporting of detection rates must account for known biases to ensure reliability.

Outlook:

• cfDNA screening may become a general population alternative to sequential screening with future cost reductions.
• Informed patient choices depend on reliable comparative performance estimates for all screening methods.
• Further research is needed to refine performance estimates and address potential biases in reporting.