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Thursday, August 21, 2014
Inherited Disorders and Birth Defects
Balanced Translocation & Pregnancy
I have lost five pregnancies, one of which resulted in a foetus with un-balanced translocation of chromosomes 7 and 21. It was lost at 19 weeks. The other pregnancies never resulted in a live foetus and were lost at 9 weeks.
During the unsuccessful pregnancy I was diagnosed with a balanced translocation of chromosomes 7 & 21 which was inherited from my mother. My husband was also diagnosed with an inverted Y chromosome. He has previously had two children (with a different wife) but she did suffer several miscarriages before the successful pregnancies.
I`ve been told that the chances of me being able to have a successful pregnancy are very slim but I`ve never been told statistically what this number might be. We are currently thinking about adoption, but deep in my heart I would like to keep trying to conceive naturally. However, I don`t know how unrealistic or realistic I am being...I need more information.
Please could you tell me what my chances of success actually are? I`m desperate to know.
The chance of having an egg that has the unbalanced translocation vs. the normal or balanced rearrangement depends on how the chromosomes line up, divide and segregate – that is how the chromosomes divide into two daughter cells. Theoretically, you have a 25% chance that the eggs that you produce – will have a normal chromosome complement, a 25% chance that the egg will have the balanced translocation (like you) and a 50% chance that the egg would produce an unbalanced chromosome complement. Usually the eggs (same thing for sperm) that produce an unbalanced complement are miscarried because they are not viable – capable of producing a live born child.
So in theory, you have a 50-50 chance of having a normal baby (either a carrier like you or not a carrier). However, what we see in real life does not always match what should happen in theory. Unfortunately, there are no specific statistics about what the chance is for a woman with a translocation such as yours to have a normal pregnancy. Researchers do not know why some women who are balanced translocation carriers miscarry more often than others.
Also in your case, because you have a translocation involving chromosome 21 – there is a chance (~10%) that you could have a baby with Down syndrome. So if you do become pregnant, you should discuss this with your doctor.
Your husband has an inverted Y chromosome, which is not uncommon in the general population. An inversion happens when there are two breaks in one chromosome. The area between the breaks is inverted (turned around or flipped). This flipped chromosomal material is then reinserted and the areas of the breaks unite to the rest of the chromosome. There is usually no effect since no chromosomal material was lost. This is the case for your husband – we know this because he has no problems and has normal fertility. However, all of his sons will inherit his inverted Y chromosome.
Perhaps with both of you having changes with your chromosomes, this has put you at higher risk to miscarry, but I do not know of any research studies that state this is the case.
Having repeated miscarriages is very stressful I am sure. Adoption certainly is an alternative in your situation. Another option would be to talk to a reproductive specialist about preimplantation genetic diagnosis (PGD). This is a type of reproductive technology that involves invitro fertilization. A reproductive specialist would be able to answer your questions and provide you with specific information about IVF for genetic indications, such as yours.
Finally, if you haven’t already done so, you may want to sit down with a genetic counselor or geneticist and talk about these risk figures specifically in regard to your chromosome rearrangement. Knowing the exact rearrangement may be helpful in giving you more precise information. The National Society of Genetic Counselors resource link can help you locate a genetics center near you.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University