Tuesday, September 2, 2014
Inherited Disorders and Birth Defects
Balanced Translocation of Chromosomes 14 & 15
My husband has been diagnosed with the above balanced transl of Chrom 14 & 15, we are now 8 weeks preg after having 2 m/carriages. Will this type of translocation generally end in misscarriage and if so what is the maximum that the fetus could survive? I guess I want to know when could we expect that we have concieved a healthy baby? We have confirmed today that the baby is still ok, heart beat at 184 bpm all looks normal so far? If we make it to 12 weeks could we be more sure that the baby is not going to miscarry due to the chromosome issue? Thx.
In theory, there is a 25% chance that the gametes (eggs or sperm) that the mom or dad produces - will have a normal chromosome complement, a 25% chance that the egg or sperm will have the balanced translocation and a 50% chance that the egg or sperm would produce an unbalanced chromosome complement. In your case, the unbalanced complement could be trisomy 14 (3 # 14 chromosomes), trisomy 15 (3 # 15 chromosomes) or a monosomy - having only 1 chromosome 14 or only 1 chromosome 15.
In all of these cases that produce an unbalanced complement - there is a very high probability (greater than 99%) that you will miscarry. There have been a few rare cases of children born with trisomy 15 that had multiple birth defects. I am not aware of any pregnancies surviving long enough to have a live born child with trisomy 14, monosomy 14 or monosomy 15.
Most pregnancies that have an unbalanced translocation miscarry early in the first trimester. However, there are some women that are good at holding on to a pregnancy, even when it is abnormal and may not miscarry until later in the first trimester or early second trimester. So it is not possible to give you an exact number of how long the fetus could survive. However, it is very highly likely, that if the pregnancy continues beyond the 12th or 13th week, and the ultrasound studies are normal, then you will not miscarry due to the translocation.
You ask excellent questions. 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. 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