Ann - I've been seeing Dr M a reproductive immunologist based in Sydney who did a range of tests on me & DH as I keep getting chemical pregnancies with CGH tested top quality blasts. The results came back that I have high natural killer cells & that DH & I have 4 HLA genetic matches. For pregnancy to occur your body has to accept the embryo as being different to self & otherwise the killer cells kill off the embryo as if it is cancer. Dr M said we have a 50:50 chance of each embryo being too closely matched (as in the 4 HLA matches). It's called allo-immune implantation dysfunction. All very confusing but there is treatment for it to basically help my body recognize all embryos as different which we will be moving onto if this cycle doesn't work.
My DD was a 5 day blast (not expanded at time of transfer).