Comparison of fetal and maternal chromosome polymorphisms: Applications in prenatal diagnosis

By comparing the polymorphisms of Q‐banded karyotypes of a mother and her female fetus, it is possible to confirm that maternal cell contamination is a rare event in prenatal diagnosis. The frequency with which any given polymorphism is distinctive is directly correlated to its prevalence in the population. Hence, since the polymorphisms on bands 3c, 13p and 21s are the most prevalent in the population, comparison of these maternal bands with the corresponding fetal ones is most likely to yield a distinctive pattern between a mother and her female fetus. However, in light of the rarity of maternal cell contamination, comparison of chromosomal polymorphisms is not cost‐effective for all cases, and is recommended only for high‐risk situations such as prenatal diagnosis of recessive or X‐linked diseases, where maternal age is over 40, or when amniotic fluid is grossly bloody.