Chromosomal abnormalities

Chromosomal abnormality refers to a missing, extra, or irregular portion of a chromosome or part of a chromosome. They occur due to an error in cell division, either during mitosis or meiosis, and they can be classified into numerical or structural anomalies.

The presence of a chromosomal abnormality is a major cause of perinatal mortality and childhood disability. The incidence of the majority of chromosomal defects increases with advancing maternal age and this incidence decreases as pregnancy advances due to the increased risk of miscarriage of fetuses with chromosomal defects. The rate of fetal death between 12 weeks and term in euploid fetuses is 1-2%; however, this rate increases to 30% in trisomy 21 (14) and is as high as 80% in trisomies 18 and 13 (1).