Implantation is the nascent pregnancy stage during (day 6 to 12) during which the embryo adheres to the wall of the uterus. It is through this attachment that the foetus receives oxygen and nutrients from the mother and grows further. In other words, unsuccessful implantation means halting the foetal growth and thereby eliminating pregnancy.
Generally, implantation occurs 6 to 8 days after the egg is fertilized. But at times, such attachment fails to happen and leads to implantation failure. An embryo may not implant when there is something inherently wrong with the embryo itself. Or something in the uterine environment may not allow a normal embryo to implant. Age of the pregnant woman is yet another common factor responsible for implantation failure. With increasing age, the numbers of eggs in the ovaries decrease.
Reason behind implantation failure
While there are several causes for implantation failure, some of them are listed below:
- Incomplete implantation: Women may have a biochemical pregnancy, with low levels of the pregnancy hormone B-HCG. Hence, a clinical pregnancy occurs with a sac and a heartbeat is never established.
- Improper embryo transfer: Majority of implantation failures can be attributed to embryo transfer. Factors like uterine preparation, proper timing, and number of embryos transferred along ensure correct embryo transfer. Any deviation in the procedures causes implantation failure.
- Poor ovarian response: Caused possibly by impaired prenatal oocyte development or low number of existing oocytes in the ovaries.
- Poor egg quality: Problems within eggs can manifest clinically as diminished ovarian reserve or premature ovarian failure.
- Poor internal environment: Anatomic, hormonal and immunologic problems within the environment in which the embryo implants and foetus grows may cause implantation failure.
- Special conditions: In some cases, cervical stenosis condition is observed where endocervical canal is narrowed or completely closed.
Also, implantation failures may occur in assisted reproductive technology methods. Other factors like ovarian hyper stimulus, weak immune system are some of the common causes of implantation failure.