It's widely accepted that chromosome abnormalities are the most common cause of miscarriages; studies show that somewhere between 50% and 75% of first-trimester miscarriages involve chromosome problems. For couples who want a definite answer on whether chromosomes played a role in a miscarriage, it's sometimes possible to order tests to analyze the baby's chromosomal makeup.
Who Should Have Testing:
Because the odds of having a successful pregnancy after one miscarriage are fairly high, doctors may not suggest chromosome testing unless a couple is experiencing recurrent miscarriages. (With multiple miscarriages, it can be beneficial to confirm or rule out chromosome factors so as to guide further testing and treatment plans.) Some parents may prefer to have testing regardless of the number of miscarriages, feeling that an explanation for the miscarriage may help in finding closure.
Collecting Tissue for Testing:
It isn't always possible to run a chromosome test, especially after a very early miscarriage, since it can be difficult to get an adequate tissue sample. If you are currently having a miscarriage and want to pursue chromosome testing, get in touch with a doctor right away for advice on how to collect and preserve the tissue. Sometimes it is easiest to have chromosome testing done if you have a D & C.
What the Results Can Show:
The testing involves counting the number of chromosomes and examining the structure. This can confirm or rule out obvious chromosome abnormalities as the cause of a miscarriage. The most common chromosomal cause of miscarriage is trisomy (present in about 41% of miscarriages). Other chromosome abnormalities might include triploidy, monosomy, tetraploidy, or structural malformations (such as translocations). Abnormalities are usually caused by sporadic abnormalities in the sperm or egg, rather than inherited from a parent.
Sometimes results showing normal chromosomes in a miscarried baby will be deemed conclusive only if the baby was a boy. Because well over half of chromosomally normal results from miscarriages tend to be female, researchers believe that it is common for the mother's tissue to contaminate the results (although careful lab techniques may reduce the odds of this occurring). For cost and feasibility reasons, it's not possible to determine whether the test results came from the mother or from the baby in these cases.
Planning for Future Pregnancies:
Regardless of the results of your test, you will most likely have questions about how to best plan for future pregnancies. A supportive doctor or genetic counselor should be able to answer your questions.
If your test results revealed a chromosomally normal baby (or inconclusive results) and you are having recurrent miscarriages, it may be wise to talk to your doctor about testing for other miscarriage causes. You may wish to see a specialist to discuss what tests would be most appropriate for your circumstances. Unfortunately there won't always be answers on the cause of the miscarriages, but it makes sense to rule out potentially treatable conditions.
If the results of your chromosome testing do reveal that your baby had an abnormality, the odds are highest that it was a random one-time problem. It does not necessarily mean that you have an increased risk of having a baby with that abnormality in the future. Most chromosome abnormalities are the result of errors in cell division of the sperm or egg, and most of the time they will not recur in future pregnancies. The exception to this rule is if the results reveal that the baby had an unbalanced translocation, in which case the doctors may recommend you and your partner be tested for a condition called balanced translocation.
In the rare case that couples have multiple miscarriages that appear to be caused by chromosome abnormalities, a procedure known as pre-implantation genetic diagnosis in combination with in-vitro fertilization (IVF) may reduce the risk of further miscarriages -- but the procedure is very expensive and usually not covered by insurance.
ACOG Education Pamphlet AP100 - Repeated Miscarriages. American College of Obstetricians and Gynecologists. Accessed: Apr 1, 2009. http://www.acog.org/publications/patient_education/bp100.cfm.
Lathi, Ruth B. and Amin A. Milki. "Tissue Sampling Technique Affects Accuracy of Karyotype from Missed Abortions." Journal of Assisted Reproduction and Genetics Nov 2002. 19(11):1573-7330 (Online)
Trisomy accounted for 41% of miscarriages: chromosomal abnormalities linked to age seen in most miscarriages. OB/GYN News. Accessed: Mar. 31, 2009. http://findarticles.com/p/articles/mi_m0CYD/is_17_39/ai_n6212351.