There are several methods available to detect early apoptosis in frozen samples. HC for EtBr/AO staining, IHC using specific antibodies of early apoptotic markers, Colorimetric assays for early apoptotic markers, ELISA for early apoptotic markers like Fas/FasL, cytocrome c, p53, bax/bcl2, upstream and downstream caspases etc; DNA ladder by Gel Electrophoresis and many more approaches are available to detect early apoptosis in frozen reproductive tissues. Its all depends on the feasibility and availability of compenents for said approaches in your lab.
If you are interested, kindly go through our lab publications (more than 50 internationals papers are available on apoptosis in reproductive cells/tissue) on research gate and PubMed for detailed protocol.
For the early apoptosis analysis, the most recommended kit is Annexin V/Pi, because is a human anticoagulant, 35 kda, ca2+ dependent phospholipids binding protein that have the high affinity with phosphatidyl serine(ps), then label with fluorophores can identify the cells at early apoptosis stage by binding with Ps exposed on the outer leaflet.
I used the Annexin /pi apoptosis detection kit and other but it is best to detect cells at early apoptosis.
Now regarding the procedure to follow, you can download prof Chitra Mandal paper.