The Los Angeles County Department of Public Health released death certificates Monday for the actresses.
Fisher, the only daughter of Reynolds and late singer Eddie Fisher, died Dec. 27, days after going into cardiac arrest on a plane Dec. 23. The Star Wars actress' cause of death was listed as "cardiac arrest/deferred," meaning there will be further investigation.
Reynolds' cause of death was listed as an intracerebral hemorrhage -- a type of stroke -- with hypertension as an underlying cause, TMZ reported. She died Dec. 28, a day after Fisher, in a Los Angeles hospital.
"She wanted to be with Carrie," Reynolds' son, Todd Fisher, told Variety at the time.
The pair are survived by Fisher's daughter, Billie Lourd, and Todd Fisher.