The sensitivity of allele-specific polymerase chain reaction can obviate concern of maternal contamination when fetal samples are genotyped for immune cytopenic disorders, ,

OBJECTIVE: Fetuses at risk for immune cytopenic disorders can be identified by molecular genotyping assays. To better understand the impact of maternal contamination on genotyping results, the levels of contamination that are routinely encountered during prenatal testing of fetal samples and the sensitivity of allele-specific polymerase chain reaction in detecting paternal alloalleles were examined. STUDY DESIGN: Reconstitution experiments were performed to define the sensitivity of allele-specific polymerase chain reaction assays. The sensitivities of allele-specific polymerase chain reactions and polymerase chain reaction–restriction fragment length polymorphism were compared for detection of the factor V Leiden mutation. RESULTS: A quantitative analysis of variable-number tandem repeat loci revealed maternal contamination in 4 of 56 fetal samples. Contaminating deoxyribonucleic acid compromised genotyping results when it comprised between 94% and 99% of the total deoxyribonucleic acid. Allele-specific polymerase chain reaction was found to be the more sensitive technique (0.8% sensitivity vs 13% sensitivity). CONCLUSION: These results illustrate that allele-specific polymerase chain reaction is well suited for reliable prenatal identification of fetuses at risk of immune cytopenic disorders.(Am J Obstet Gynecol 1997;176:327-30.)