Parental Karyotype Tests for Recurrent Miscarriages

Taking a Picture of Chromosomes to Diagnose Pregnancy Loss

Couple in a consultation with a doctor
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There's no question it can be devastating to lose a pregnancy. In fact, nearly 15 percent of pregnancies end spontaneously early on, research shows. For most couples, a miscarriage happens just once and then they are able to go on and have healthy, happy babies. 

However, if a couple has recurrent miscarriages there may be any number of reasons for the multiple losses, such as an anatomical abnormality in the woman's reproductive organs; a blood clotting disorder; or hormonal problems. Infections, environmental factors, and advanced age of either or both parents also are thought to play a potential role in recurrent pregnancy loss. 

In about 4 percent of couples who have recurrent miscarriages, the problem may be some sort of chromosome abnormality in one or both partners. A test called a karyotype can be used to confirm if this is the case. 

Chromosomes Illustrated

A karyotype is a picture of a person's chromosomes, the "packages" of genetic material called DNA that exists within the nucleus of every cell in the body. Normally, human cells have 46 chromosomes arranged in 23 pairs. A karyotype test can detect deviations from that number as well as abnormalities in the way each chromosome is formed.

In order to obtain a parental karyotype, blood (usually white blood cells) from both or either parents is used. (Sometimes tissue from the lost pregnancy is tested.) From the blood cells, the chromosomes are isolated, stained, and examined under a microscope. A picture of the chromosomes also is taken through the microscope. 

This picture is then cut up and the chromosomes are organized according to size, from largest to smallest. An expert called a cytogeneticist can then examine the completed karyotype to look for missing or extra pieces of chromosome that may play a role in the recurrence of miscarriages.

Parental Karyotypes and Miscarriage Risk

Although underlying chromosome issues affect only a small number of couples having recurrent miscarriages, some physicians include parental karyotyping as a routine test for couples who have had multiple miscarriages.

Other doctors use the test only for couples with an increased risk of having a chromosome-related condition. It's common to test both parents. The most typical type of chromosomal problem in these couples is balanced translocation, meaning parts of certain chromosomes are rearranged. A karyotype may also reveal other types of translocations or a condition called chromosomal mosaicism.

Why don't all doctors routinely order parental karyotypes for couples who have recurrent pregnancy loss? Simply because regardless of what the test shows, most couples will continue to try to conceive and have a successful pregnancy regardless of what the karyotype shows. A chromosomal abnormality isn't a guarantee a pregnancy won't be normal.

In Vitro Fertilization and Miscarriage Risk

Couples who have a karyotype test that reveals chromosomal abnormalities can get guidance from a genetic counselor as to how to proceed in the pursuit of a normal pregnancy. One possible avenue is in vitro fertilization (IVF)–a time-consuming and invasive fertility treatment that involves removing eggs from a woman's ovaries to be fertilized in a lab. The embryos that result are then implanted into the woman's uterus.

For prospective parents dealing with chromosomal issues, IVF is coupled with a procedure called pre-implantation screening (PSG) in which chromosomes from the embryos are examined for abnormalities such as aneuploidy, in which there is an extra or missing chromosome. For example, Down Syndrome can occur when there is an extra copy of chromosome 18 or 21.

Aneuploidy embryos are more likely to fail to implant or end in miscarriage. If implantation, pregnancy, and birth take place, aneuploidy embryos may result in a child with mental or physical disabilities. Embryos found to have abnormalities, therefore, are not implanted. 

These procedures may speed up the process of having a normal pregnancy, and some doctors do support using them. However, they may be prohibitive for many couples because they're invasive expensive, and often not covered by health insurance. 

Actually, research shows that compared to couples who use IVF, couples who keep trying with no intervention have about the same odds—around 71 percent—of eventually having a normal pregnancy. 

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