Taisia Osipova, the wife of an activist with the Other Russia political party, had been sentenced to 10 years in prison on drug charges, a term that members of the opposition called excessive.
Medvedev addressed her case at a meeting with Moscow State University journalism students in January, promising to ask prosecutors to review it.
At a hearing on Tuesday, a judge ordered that Osipova remain in jail until June 15 while her case is being reexamined.
Her supporters contend that she should be released from pre-trial detainment because she suffers from diabetes, among other illnesses, and has a young child.
Osipova's lawyer Svetlana Sidorkina said they will appeal the judge's decision.