More than half of allmiscarriages are caused by chromosome problems in the baby. In most cases, these problems arise during formation of the sperm or egg rather than being inherited from the parents, so the odds are good that the next pregnancy will not be affected by chromosome issues. But about 4% of couples with recurrent miscarriages have chromosome abnormalities in one or both parents that can recur in future pregnancies, so some doctors suggest parental karyotype tests as a part of investigating recurrent miscarriage causes.
What Karyotype Tests Are:
A karyotype test is not a comprehensive test for every known genetic disorder. Instead, the test involves evaluation of the number and structure of the chromosomes. Human cells are supposed to have 46 chromosomes (23 pairs), so a karyotype test can detect deviations from that number as well as abnormalities in how chromosomes are formed. From a miscarriage perspective, karyotypes may be performed on prospective parents to detect underlying issues or they may be performed on tissue from the pregnancy to detect issues present in a specific baby.
Parental Karyotypes and Miscarriage Risk:
Underlying chromosome issues affect only a very small number of couples having recurrent miscarriages. The most common conditions in these couples is balanced translocation, meaning parts of the chromosomes are rearranged and usually with no outward symptoms. A karyotype may also reveal other types of translocations or a condition called chromosomal mosaicism.
Who Should Have the Test:
Some doctors include parental karyotyping as a routine test for couples having multiple miscarriages, whereas others never order the test, and other doctors use the test only for couples whom they believe have a higher risk of having a chromosome-related condition (such as parents with more than one miscarriage proven to be affected by a specific abnormality). Usually both parents are tested, as chromosome problems may originate in the father as well as in the mother.
What the Results Mean for Future Pregnancies:
A big reason why many doctors do not order parental karyotypes routinely is that even if an abnormality is found, there really isn't anything that can be done about it. The most common plan for couples with abnormal karyotypes is to keep trying.
The one possible treatment in these cases is to attempt IVF with pre-implantation genetic testing of the embryos. But using intervention does not appear to change the ultimate outcomes. IVF can work in these cases and may speed up the process of having a normal pregnancy, and some doctors do support using it, but IVF is also invasive, expensive, and frequently not covered by health insurance. And research shows that, compared to couples who use IVF, couples who keep trying with no intervention have about the same odds (around 68%) of eventually having a normal pregnancy.
Thus, given that couples with a proven chromosome issue will simply be advised to continue trying normally, the value of parental chromosome testing is debatable. Still many doctors (and prospective parents) prefer to have as much information as possible. If you do have the test performed and receive abnormal results, a genetic counselor can probably help you figure out where to go from here. On the other hand, if the results are normal, you will know that there is no known chromosome disorder affecting your odds of a successful pregnancy.
Stephenson, Mary D. and Sony Sierra. "Reproductive outcomes in recurrent pregnancy loss associated with a parental carrier of a structural chromosome rearrangement." Human Reproduction 2006 21(4):1076-1082.
Sugiura-Ogasawara, Mayumi and Kaoru Suzumori. "Can preimplantation genetic diagnosis improve success rates in recurrent aborters with translocations?" Human Reproduction 2005 20(12):3267-3270.
Using Karyotypes to Predict Genetic Disorders. University of Utah Genetic Science Learning Center. Accessed: May 16, 2009. http://learn.genetics.utah.edu/content/begin/traits/predictdisorder/.