We used Multiple-Cause Mortality Files (MCMF) compiled by CDC’s National Center for Health Statistics for 1983 through 1997. MCMF include demographic information and International Classification of Disease, Ninth Revision (ICD-9) codes for the underlying cause of death and up to 20 conditions listed on the death certificates of more than 32 million people who died in the United States during this period.

We selected all cases that contained code 758.0 (Down syndrome) anywhere in the record, but we excluded cases that also contained code 779.6 (pregnancy termination) and had age=0.