The young healthy couple having regular unprotected intercourse may expect a pregnancy in about 30% of cases within 3 months, almost 60% within 6 months and in 85% after 12 months. The question has to be asked, if everything is completely normal and with intercourse in the fertile window, why is a pregnancy not achieved in every cycle? As this process is biological and not mathematical and the mechanisms of ovulation, tubal transport, sperm physiology and implantation are so complicated, one can only marvel that pregnancies are achieved spontaneously so frequently!
During in-vitro fertilisation (IVF) we can help these processes considerably; ovulation is stimulated with medications, tubes are completely bypassed and a single healthy sperm can be isolated and injected into the egg. And yet, pregnancy rates are from 100%. The reason for this is the problem of successful implantation into the lining of the womb when the embryo is placed into the cavity of the womb. Herein are secrets that have not yet been revealed. We know that aged eggs will not implant and embryos that have abnormal chromosomes are ‘refused entry”. What factors decide which embryos will be accepted for implantation and will grow into a viable foetus?
This appears to be shared by the quality of the egg and the ‘receptivity’ of the lining of the womb (endometrium). In the endometrium, there are a myriad of factors that aid implantation. All have to be in place and active at the right time in order for implantation to occur. It is now obvious that there is some crosstalk between the fledgling embryo and the endometrium, a sort of application interview for acceptance.
Repeated implantation failure is a most frustrating situation. There is some evidence that the hormone environment has a part to play but the puzzle is far from solved and presents an enormous challenge for researchers.
Anil Gudi, Amit Shah & Roy Homburg