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If the IVF and IUI treatments have failed, then chances of problems occurring with the acrosomal protein (protein in head part of sperms responsible for penetration into egg for fertilization) could be the problem. In these cases, ICSI (intracytoplasmic sperm injection) can be tried.
Other possibilities of failure include scars in uterus, which can pose problems in successful implantation and formation of placenta. This can be detected with help of HSG (hysterosalpingogram) to visualize interior of the uterus and look for scar tissue.
Discuss about these possibilities and getting these further tests done with your treating gynecologist to help you with getting pregnant. Take diet rich in foods containing zinc to help with good quality of egg and sperms maturing. Be stress free especially during intercourse to have normal hormonal levels required for successful pregnancy.
Take care.