ABSTRACT
Genetic factors are the most common causes of spontaneous miscarriage. Half of first trimester clinical miscarriages show numerical chromosomal abnormalities. Pregnancy loss is also associated with single-gene mutations, but far less is known concerning the role single genes play in spontaneous miscarriages. The additional chromosome results in a small additional amount of DNA specific for the trisomic chromosome in maternal plasma; however, this is enough to differentiate a euploid form an aneuploid pregnancy. The number of chromosome 21 transcripts in a sample can be compared to number expected in a reference DNA sample known to be from or representative of a normal individual. A maternal age effect is evident in most trisomes, but the relative effect varies among chromosomes. Maternal age correlates positively with errors at meiosis I, the assumed cytological explanation for most autosomal trisomies. The relative proportion of trisomies arising at meiosis I versus those arising at meiosis II varies among aneuploidies.
