Current Options for Paternity Testing
Paternity testing can be performed through three main approaches: traditional postnatal testing using blood/tissue samples, non-invasive prenatal paternity testing (NIPPT) using maternal plasma, and invasive prenatal testing via amniocentesis or CVS.
Postnatal Paternity Testing (After Birth)
The standard approach uses DNA from blood, buccal swabs, or tissue samples analyzed through:
- Short Tandem Repeats (STRs): The traditional gold standard, though can be problematic with degraded samples or chromosomal abnormalities 1
- Single Nucleotide Polymorphisms (SNPs): Increasingly used with high accuracy (>99.99%) using panels of 176+ SNPs with high minor allele frequency 2
- Combined approaches: Newer methods integrate multiple marker types for enhanced reliability
For low-template or degraded DNA samples (formalin-fixed tissues, bone specimens, old stains), probabilistic genotyping software like EuroForMix provides significantly higher likelihood ratios than standard analysis, particularly in highly degraded samples 1.
Non-Invasive Prenatal Paternity Testing (NIPPT)
This represents the most significant advancement, allowing paternity determination from maternal blood as early as 7 weeks gestation without risk to the fetus:
Technical Approaches:
- SNP-based panels: Using 861-5180 autosomal SNPs with next-generation sequencing, achieving log(CPI) values from +34 to +85 for true fathers versus below -150 for unrelated individuals 3, 4
- Microhaplotype panels: 45-plex systems combining advantages of STRs and SNPs, providing robust relationship inference with Log10LR > 10 5
- DIP-STR markers: Deletion/insertion polymorphism-STR combinations showing only 6% false negative rate in first trimester, requiring just 7 fully informative markers for determination 6
Key Advantages of NIPPT:
- Can be performed from 7 weeks gestation through delivery 6
- No risk to fetus (avoids amniocentesis/CVS complications)
- Superior for chromosomal abnormalities: SNP-based NIPPT is particularly advantageous when the fetus has trisomy 21 or other aneuploidies, as STR analysis becomes confounded by tri-allelic patterns and requires manual locus exclusion, reducing CPI by 2-21 fold. In contrast, SNP methods using allele counting produce robust results without adjustment 4
- Quantitative analysis possible: Bayesian network algorithms (KinMix) enable quantitative likelihood ratio calculations and can address complex scenarios like surrogacy or absent alleged fathers 7
Invasive Prenatal Testing
When NIPPT is unavailable or inconclusive:
- Amniocentesis (typically after 15 weeks)
- Chorionic villus sampling (CVS) (10-13 weeks)
These should be avoided when possible given the procedural risks and higher costs compared to carrier testing or NIPPT 8. The guideline emphasizes that unnecessary invasive procedures may be performed when biological fathers cannot access carrier screening, representing suboptimal care 8.
Clinical Recommendations for Timing
The optimal sequence prioritizes preconception carrier screening, but when testing occurs during pregnancy, concurrent testing of both parents is preferred over sequential testing, especially after 14 weeks gestation 8. This approach:
- Minimizes time delays in decision-making
- Reduces unnecessary invasive procedures
- Optimizes cost-effectiveness
- Allows consideration of reproductive options
Common Pitfalls to Avoid:
- Don't rely solely on STRs for aneuploid fetuses: Switch to SNP-based methods 4
- Don't perform sequential testing late in pregnancy: Test both parents concurrently 8
- Don't use standard analysis for degraded samples: Employ probabilistic genotyping software 1
- Don't assume NIPPT requires second trimester: Modern methods work from 7 weeks 6
The insurance coverage framework should recognize that paternal testing for fetal diagnosis is appropriately reimbursed through maternal insurance when fetal testing itself would be covered, as this represents the safest and most cost-effective diagnostic pathway 8.