Non-invasive prenatal testing for trisomy 13: more harm than good?

Area of Science:

• Prenatal diagnostics
• Genetics
• Maternal-fetal medicine

Background:

• A 35-year-old primigravida, pregnant via in-vitro fertilization, received a high trisomy 13/trisomy 18 (T13/T18) risk score (1:55) from first-trimester screening.
• She opted for non-invasive prenatal testing (NIPT) at 14 weeks' gestation, which indicated a positive result for T13.

Observation:

• Following genetic counseling, the patient underwent amniocentesis for definitive diagnosis.
• Quantitative fluorescence polymerase chain reaction (QF-PCR) and full karyotyping revealed a normal male karyotype (46,XY), indicating a false positive NIPT result for T13.

Findings:

• Literature review indicates NIPT for T13 has a 91.6% detection rate and a 0.097% false-positive rate.
• Hypothetical calculations demonstrate that the positive predictive value of NIPT for T13 is significantly influenced by disease prevalence.

Implications:

• The positive predictive value for T13 NIPT can be unfavorable in the general population due to low prevalence, potentially leading to unnecessary invasive procedures.
• This case highlights the importance of considering NIPT performance metrics and individual patient risk factors in prenatal genetic screening and counseling.