Home HealthTopics Health Centers Reference Library Research
Join us on Facebook Join us on Facebook Share on Facebook

Inherited Disorders and Birth Defects

Trisomy 18



Hi, I`m 32 weeks pregnant with twin boys (not sure if identicle). I had a amnio done on the much smaller baby (one is about 3 pounds, the other 2 pounds), witch tested positive for Trisomy 18. I was told that he wouldn`t survive even a day. Could the other baby have the same problem? Should I get an amnio for him too? He has appeared normal, including size, in all the ultrasounds?


It is very unlikely that the other baby has trisomy 18 (3 copies of the #18 chromosome), unless they are identical, then it is much more likely that both babies are affected. Usually, when an amniocentesis is done to examine the chromosomes and there are twins present, the doctor does 2 amniocentesis procedures to obtain amniotic fluid from both sacs. However, if there is only one sac, that would mean the twins are identical.

Also, while most babies with trisomy 18 are either stillborn or die within the first few weeks of life, not all infants born with trisomy 18 die right away.

These are very important questions. If you have not already spoken to a genetic counselor or geneticist, I would highly recommend that you do. You can locate a genetics center near you at the National Society of Genetic Counselors’ Resource Center through the website below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University