Hello there, Thanks for writing in. I learnt from your writing that you have so far undergone 4 ivf cycles which were unsuccessful. Let me help you understand in this scenario the meaning of implantation failure . When pregnancy test comes negative in two or more ivf cycles where 6 or more reasonably good quality embryos are transferred then it is assumed to be implantation failure which means the embryo has failed to get burried in the soil(which is endometrium). When the embryo is transferred, the endometrium needs to receive it with the help of finger like microscopic structures to help it get burried . And the endometrium can do it only within a very short time frame, usually 6 to 7days post ovulation. Sometimes this timeframe within which it can receive seems to be shifted either early in the cycle or later. By doing an ERA(Endometrium receptivity array) test we are able to predict this timeframe much precisely so that the embryo transfer can be timed accordingly. 2. The size of the uterus doesn t matter for pregnancy unless its extremely small. 3. Progynova is not being used for increasing the size of uterus. Hope your question is satisfactorily answered. Good luck.