USCIS is revising policy guidance for the validity period of Form I-693, Medical Examination. The updated policy goes into effect on November 1, 2018, and will require applicants to submit a Form I-693 signed by a civil surgeon no more than 60 days before filing.
The Form I-693 will remain valid for a 2-year period following the date the civil surgeon signed it (not submitted, but signed).
Read here.