I'm pregnant with my second child and just recently had an ultrasound. They found a spot on the baby's heart. I decided to have amniocentesis done to detect Down syndrome. My aunt has a baby with Down syndrome, and I'm wondering—what are my odds of having a baby with Down syndrome because it is in the family? I'm 30 years old.
The spot you describe that was recognized by ultrasound in the fetal heart is called a hyperechogenic focus. Our knowledge today indicates about a 1 percent risk for this feature to be associated with a chromosome disorder such as Down syndrome. The amniocentesis and subsequent chromosome studies on the cultivated amniotic fluid cells will accurately determine whether or not the fetus is affected.
There are three chromosome types of Down syndrome, the most common being due to an extra chromosome 21 (called trisomy 21). This type accounts for some 94 percent of all those born with Down syndrome. About 3 to 4 percent are born with a chromosome rearrangement involving chromosome 21 (called translocation Down syndrome), while 3 to 4 percent of babies born with Down syndrome have a mixture of normal cells and those with trisomy 21 (called Down syndrome mosaicism). You need to find out precisely which type of Down syndrome your aunt's baby has. This would be especially important for translocation Down syndrome, since that is the type that is transmitted through the family. That could be very important for you in this and any other future pregnancy.