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Miscarriage, Aneuploidy and Preimplantation Genetic Screening
Chromosomes are the cells in our body that carry genetic information in the form of DNA. Each healthy person normally has 23 pairs of chromosomes (a total of 46). There are 24 types of chromosomes: 22 pairs of autosomes numbered from one to 22 and one pair of sex chromosomes (XX or XY). A femaie has a pair of XX chromosomes, and a male has an XY pair of chromosomes.
What Is Aneuploidy?
The term aneuploidy is used to describe an abnormal number of chromosomes. Normally, an egg has 23 chromosomes, and the sperm has 23 chromosomes so that the resulting embryo has a total of 46 chromosomes – half from the mother and half from the father. However, sometimes an egg or sperm may have an abnormal number of chromosomes, which results in an embryo with aneuploidy. The majority of embryos with aneuploidy will not implant in the uterus or will result in a miscarriage. The majority of first trimester miscarriages are the result of aneuploidy.
There are cases, however, in which a baby can be born with an abnormal number of chromosomes. One of the most common examples of this is Down syndrome, which is caused by having three copies of chromosome 21 (Trisomy 21). An extra copy of a chromosome is called a 'trisomy.' A missing copy of a chromosome is called 'monosomy.'
Aneuploidy can happen in any pregnancy, but the chances increase as a woman ages. Because many embryos with aneuploidy are miscarried, the chances of miscarriage also increase as a woman ages.
PGS Holds Promise for Recurrent Miscarriage
Preimplantation genetic screening (PGS) in conjunction with in vitro fertilization (IVF) may help women with advanced maternal age or those who have experienced recurrent miscarriage increase their chances of having a successful pregnancy and healthy baby. New genetic testing techniques such as array CGH allow testing on all of the chromosomes for aneuploidy with results returned in time for an embryo transfer with no need for embryo freezing. PGS allows fertility doctors to transfer embryos with no detectable chromosome abnormalities to the mother's uterus.
PGS for aneuploidy may be a consideration if the woman is age 35 or older, if the couple has had a previous pregnancy with a confirmed chromosomal abnormality, for couples who have had multiple early miscarriages and for couples who have had multiple unsuccessful IVF cycles. Couples with a history of three or more miscarriages should probably have their own chromosomes evaluated with a blood test to find the presence of inherited chromosome rearrangements. A balanced chromosome rearrangement does not affect your health, but it does increase the risk of having aneuploidy that can result in early miscarriage.
With recent advances in genetic testing technology, researchers expect that there will be great benefit for PGS used help achieve pregnancy success for older mothers and those who experience recurrent miscarriage.