Most people have heard of Down syndrome (trisomy 21), and most are aware that it is a chromosome disorder that causes cognitive impairments and other health concerns. One thing you may not know about Down syndrome is that it can also be a cause of miscarriage and stillbirth. Researchers estimate that as many as 80% of babies conceived with trisomy 21 are miscarried or stillborn, and trisomy 21 may cause as many as 2% of all miscarriages and 1% of all stillbirths. These numbers do not factor in elective terminations of these babies.
Researchers do not know why some babies with Down syndrome are miscarried while others are born as viable babies. Genetic factors may lead to the condition being incompatible with life for some babies but not others.
If you had chromosome testing done after your miscarriage and have received test results showing that the baby you miscarried had Down syndrome, know that the miscarriage was not your fault. Most chromosome disorders, including Down syndrome, are believed to be the result of random problems in cell division. Most of the time, there is only about a 1% chance of having a subsequent pregnancy affected by Down syndrome. If you are over 35, it's true that your odds go up of having a baby with a chromosome disorder, but the odds are higher of having a baby without a chromosome disorder.
If you are currently pregnant and have learned that your baby has Down syndrome (and you intend to continue the pregnancy), it's unfortunate but true that there is an increased risk of pregnancy loss -- but the most likely outcome is still that your baby will make it to term, albeit with the expected special needs. You may be referred to a high risk pregnancy specialist for increased monitoring for the duration of your pregnancy.
Down syndrome. March of Dimes. Accessed: Apr 6, 2009. http://www.marchofdimes.com/pnhec/4439_1214.asp.
Morris, J. K., N. J. Wald, H. C. Watt. "Fetal loss in Down syndrome pregnancies." Prenatal Diagnosis 1999. 19(2): 142-145.
Trisomy 21 Mosaicism. University of British Columbia. Accessed: Apr. 7, 2009. http://www.medgen.ubc.ca/robinsonlab/mosaic/specific/trisomy21.htm.