If unknown causes result in several miscarriages, or implantation cannot be detected with several embryos, it may be advisable to examine the lining of the uterus (the endometrium) to clarify any issues.
The thickening of the endometrium is influenced by various - above all hormonal - factors throughout the menstrual cycle, leading to structural and functional changes. In the different phases, cell function and the production of cell components and proteins varies. The ‘blueprints’ for this are found in the genes, which have different activities depending on the point in the cycle. A certain gene expression profile is typical at the time of embryo implantation, marking the implantation window, which is generally 6 days after ovulation.
In rare cases, the implantation window can be shifted forwards or backwards. This can be determined by taking an endometrial biopsy after the endometrium has been hormonally prepared to become receptive, or during a spontaneous cycle. The short intervention does not require anaesthesia and is undertaken at the point in time when normally embryo transfer would take place. The biopsy is then genetically analysed by the so-called ERA (Endometrial Receptivity Array) Test.
If the implantation window turns out to be offset, the embryo transfer time must be adjusted accordingly.
In rare cases, successful embryo implantation may be hindered by chronic inflammation of the uterine lining (endometritis) or by disturbed bacterial colonisation of the endometrium. These pathologies can also be diagnosed by genetic testing of the endometrium. A biopsy is taken simultaneously with sampling endometrial tissue for the ERA test and is subjected to triple analysis called EndomeTRIO.
A deficiency in lactobazilli may be corrected with vaginal suppositories. If chronic inflammation is detected, antiobiotic therapy specific to the pathogen spectrum is indicated.