No responses yet so will describe process.
Just over half of embryos reaching pipping stage are unable to proceed with unzipping top. Those not able to unzip usually dead within 36 hours of pipping. What I have started to do is embryos not progressing after 12 hours is basically unzip the shell for them. Then part of the membrane around head area is removed. Some bleeding usually occurs but rapidly ceases. A couple hours later I pull bill so head comes completely of the of egg. Warm water is then placed in egg to float lubricate chick. The egg is then re-positioned so chick can do balance of extrication itself which usually occurs within a couple of hours. Immediate pulling of entire chick usually results in a lot of bleeding and often death.
Part of problem likely caused by poor moisture management in latter stages of incubation. Hatch rate under hens much higher. During unzipping phase embryo turns within the shell separating self from membrane. Blood also normally stops during this turning or just before it commences preventing the bleeding noted above. Balance of yolk also brought into abdomen.
Of particular interest is the uric acid like material left in residual membrane.
