Understanding Down Syndrome Risk in Pregnancy: What to Expect

Question
My daughter is 33 and 18 weeks along in her pregnancy with her first child. Her husband who is 37 is so excited as they have been married 1 1/2 years and were trying. Well, she just went for an hour long ultra sound yesterday and they said it was a boy and everything looked fine. Her doctors office called today and said they found something wrong. She has a 1 in 9 chance of having a downs syndrome baby.  They are sending her to a specialist for more testing. What tests are considered to have possible miscarriage problems. I know a lot come back false positive but 1 in 9 chance seemed very high to me. She is afraid to tell her husband as he is a perfectionist and is afraid he will be very upset (mad). He is not an abuser but I was shocked when she said he didnt want any retarted puke kid yesterday before the test. Now what kind of man says that?  I need to know at this point what the odds are as I want to plan on being there for her should the results come back positive.  I understand this is a tough question to answer but in general what can you tell me.

kathy wilson

Answer
At 18 weeks gestation, a sonogram can only give "soft signs" of Down's syndrome and they are far from definitive. Signs of nucah luscency and other sonographic evidence can point towards chromosomal abnormalities and the patient is then sent for definitive testing. You did not mention it, but she may also have had an alphafetoprotein test, which is a blood test that also can give the risks for neural tube defects (spina bifid, anencephaly) if it is elevated, or Down's syndrome, if it is decreased. Then we recommend amniocentesis. This is the definitive test where we take some fluid from the amniotic sac (surrounding the baby) and grow it. We than can get a karyotype, telling us the number of chromosomes , the sex of the baby, and whether there are any abnormalities in the chromosomes. The risk of Down's syndrome at the age of 30 is 1:2700 pregnancies. The risk of Down's syndrome at the age of 35 is 1:350 pregnancies. The risk of Down's syndrome at teh age of 40 is 1:100. So you see that as a woman ages the risks rise logarithmically. The risk of miscarrige from the procedure is 1:400. So we usually do not recommend the procedure to all woman until the risk of the disease is greater than the risk of the procedure. Therefore, we usually do not recommend the amniocentesis until she is 35 years old. Howeveer, if the sonogram shows some "soft signs" of Down's syndrome or if the alphafetoprotein level is suspicious, we offer amniocentesis. Thousands of amniocenteses are done with no problems and it does give peace of mind. Don't be too angry at your son-in-law. It is quite a difficult concept to think of a chromosomally abnormal infant, althoough they are usually very, very loving individuals and much progress has been made over the years in the management of Down's syndrome. However, they are, indeed, dependent throughout their lives on their parents and, in many instances, must be institutionalized. Often there are other medical problems (cardiac, etc). If she does the amniocentesis and finds out the results, informed choices can be made early enough. Good Luck to you.