What are the chances of having a child with Trisomy 13 (Patau syndrome)?

Trisomy 13 (Patau Syndrome) Risk Assessment

The risk of having a child with Trisomy 13 (Patau syndrome) is approximately 1 in 12,000 live births, making it a rare chromosomal abnormality with high mortality rates. The prevalence of Trisomy 13 is significantly lower than that of Trisomy 21 (Down syndrome), with a positive predictive value (PPV) of only 37.2% even with modern screening methods. 1

Age-Related Risk Factors

• Maternal age is a significant risk factor for Trisomy 13, with risk increasing in women of advanced maternal age (35 years and older), similar to other autosomal trisomies 1
• However, unlike Trisomy 21, some population studies have noted a declining trend in Trisomy 13 prevalence in mothers aged 35 and older in recent years, though the reasons for this are not fully understood 2
• The baseline risk for Trisomy 13 is approximately 1 in 12,000 live births, which is about 10 times lower than the prevalence of Trisomy 21 3

Screening Performance and Detection Rates

• Noninvasive prenatal screening (NIPS) provides the highest detection rate for Trisomy 13 at 92.85% (95% CI = 81.15%-97.5%) with a very low false-positive rate of 0.04% (95% CI = 0.02%-0.08%) 1
• The positive predictive value (PPV) for Trisomy 13 is significantly lower than for Trisomy 21, at only 37.2% (95% CI = 26.1%-50.0%), largely due to the lower prevalence of the condition 1
• Traditional screening methods have much lower detection rates for Trisomy 13, with the FASTER trial showing only 44% detection, and these cases were typically detected only when they had screened positive for Trisomy 21 or 18 1
• ACMG strongly recommends NIPS over traditional methods for trisomy screening, including Trisomy 13 1

Factors Affecting Screening Accuracy

• Certain pregnancy factors can interfere with NIPS performance, including:
  • Vanishing twin gestations, as aneuploidy is common in early embryonic demise 1
  • Maternal malignancies, which can cause somatic genomic aberrations that may be detected with NIPS 1
• The source of cell-free DNA in maternal circulation is primarily maternal (about 90%), with only about 10% derived from placental trophoblastic cells, which can lead to discordant results 1
• Discordant results between NIPS and diagnostic testing may be due to confined placental mosaicism, resorbed twin pregnancies, or variations in maternal DNA contribution 1

Natural History and Outcomes

• Trisomy 13 is associated with high mortality rates, with approximately 90% of affected infants dying within the first year of life 4
• A population-based study found that the median survival time for children with Trisomy 13 was 12.5 days (IQR 2-195 days) 5
• The 1-year survival rate for Trisomy 13 was 19.8% (95% CI, 14.2%-26.1%), and the 10-year survival rate was 12.9% (95% CI, 8.4%-18.5%) 5
• An estimated 70% of Trisomy 13 fetuses alive in the second trimester will be spontaneously lost by term 1

Diagnostic Confirmation

• NIPS is a screening test, not a diagnostic test; positive results should be confirmed with diagnostic testing 1
• The American College of Medical Genetics and Genomics (ACMG) recommends chromosome analysis via chorionic villus sampling (CVS) or amniocentesis for definitive diagnosis of Trisomy 13 1
• Chromosomal microarray (CMA) may be considered as a follow-up test after chromosome analysis to evaluate for structural arrangements that may inform recurrence risks 1

Clinical Implications and Counseling

• Parents should be counseled that Trisomy 13 is associated with severe congenital abnormalities affecting multiple organ systems 4
• While early mortality is the most common outcome, approximately 13% of children with Trisomy 13 may survive for 10 years 5
• Among children who undergo surgical interventions, 1-year survival after surgery is approximately 70.7% (95% CI, 54.3%-82.2%) 5
• The high rate of prenatal diagnosis and termination has led to a decrease in live-born prevalence of Trisomy 13 from 0.05 to 0.03 per 1,000 live births in some populations 6