The Role of Parental Karyotyping for Diagnosing Recurrent Miscarriage

Couple in a consultation with a female doctor

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There's no question that it can be devastating to lose a pregnancy. As many as 15% to 24% of detected pregnancies end spontaneously (many more miscarriages occur so early that a woman does not yet know she is pregnant). For most couples, a miscarriage happens just once and then they are able to go on and have healthy, viable pregnancies. 

However, if a couple has recurrent miscarriages, there can be many 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 some 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. 

What Is a Karyotype and What Does It Tell Us?

A karyotype is a picture of a person's chromosomes, the packages of genetic material that exist 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 one or both parents is used. Sometimes tissue from a 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? Regardless of what the test shows, most couples will have a successful pregnancy. A chromosomal abnormality isn't a guarantee that a pregnancy will fail. Recurrent miscarriages can only be attributed to chromosomal abnormalities about 4% of the time.

In Vitro Fertilization Following Recurrent Miscarriages

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 viable pregnancy. One possible avenue is in vitro fertilization (IVF), a fertility treatment that involves removing eggs from a woman's ovaries to be fertilized in a lab. The embryos that result are then transferred to the uterus of the intended mother or a surrogate.

For prospective parents dealing with chromosomal issues, IVF can be coupled with a procedure called pre-implantation screening (PGD). In this process, chromosomes from 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.

Embryos with aneuploidy are more likely to fail to implant or to develop, which leads to miscarriage. If implantation, pregnancy, and birth do take place, the child may be born with disabilities. Embryos found to have abnormalities, therefore, are not transferred. 

Some research shows that compared to couples who use IVF, couples who keep trying with no intervention have about the same odds—around 71%—of eventually having a viable pregnancy. But IVF with PGD may speed up the process (if the reason for recurrent miscarriage is repeated chromosomal abnormality) significantly. It could take four months or less to conceive with this assistance, versus as long as six years without it.

Pursuing IVF with PGD may be difficult for couples because the process is invasive, time-consuming, expensive, and often not covered by health insurance. But in women over 35 years old, time is of the essence and it may be impractical to try to conceive without help. In addition, the odds of miscarriage drop significantly with IVF-PGD, which can be important for couples emotionally.

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