What is a Chromosome Disorder and what is its Significance?

Miscarriages in the first trimester of pregnancy are relatively common, and occur in approximately 20-25% of pregnancies. The causes of miscarriages are multiple, and cover a range of factors associated both with the fetus and the mother. Fetal causes include chromosome disorders and syndromes, non-chromosomal genetic disorders, and abnormal fetal development. Maternal factors include chronic illnesses, viral infections during pregnancy, abnormalities of the uterus, etc. There are also many factors that are as yet unknown.

Abnormal fetal chromosomal structure is one of the most common causes of miscarriage. Usually this is a new occurrence arising in the fetus, but in a small number of cases it is the result of a chromosomal problem in one of the parents. Here the parent carries a structural change in one of his/her chromosomes in a balanced manner (a translocation or inversion). The parent is completely healthy, because there is no change in the total amount of genetic material, but the fetus may receive an unbalanced chromosomal complement (insertions or deletions of complete chromosome segments or whole chromosomes). In some cases, the change causes a miscarriage.