USCIS is updating policy guidelines that a I-693 is valid for 2 years from the date the doctor signed it. This policy is supposed to go into effect from November 1st of 2018. I am not sure if this includes applications which were filed with an I-693 prior to November 1st 2018 but this is welcome news as it avoids the need to go get medical checkups every year while waiting
Quoting the page partly
USCIS is revising policy guidance for the validity period of Form I-693, Report of Medical Examination and Vaccination Record.
The updated policy, which goes into effect on Nov. 1, 2018, will require applicants to submit a Form I-693 that is signed by a civil surgeon no more than 60 days before filing the underlying application for an immigration benefit. The Form I-693 would remain valid for a two-year period following the date the civil surgeon signed it. As such, USCIS is retaining the current maximum two-year validity period of Form I-693, but calculating it in a different manner to both enhance operational efficiencies and reduce the number of requests to applicants for an updated Form I-693.