The uterus may perform quality control tests on a fertilized egg before determining if it wants to accept the embryo, according to new research. A team of scientists from the UK Universities of Southampton and Warwick and the University of Utrecht in the Netherlands found that the endometrium, or lining of the uterus, would not allow a fertilized egg to embed itself if the uterus does not sense specific chemical signals from the egg.
One such chemical signal comes from the common enzyme, trypsin. The lack of trypsin seems to indicate the quality of the embryo is not high. If the endometrium does not sense trypsin, the uterus will not accept the egg. The egg will disintegrate and the menstrual cycle will begin again.
These results are important to couples trying to get pregnant through IVF, but one of the major problems with the procedure is getting fertilized eggs to implant in the endometrium. Understanding why the uterus accepts some eggs and not others can help improve treatment and success rates.
For this study, scientists cultured fertilized eggs as normal in a dish with a special fluid that helps embryos grow. The researchers added endometrial stromal cells, a type of unhealthy cell sometimes found in the endometrium, before incubating the fertilized eggs. Scientists then assessed the reaction of the genes in the endometrium when exposed to the embryos. The team noted almost no reaction to the media containing good embryos but saw a big reaction to “bad” embryos.
The research team found the same thing happened after implanting eggs in animals. The scientists repeated the experiment but implanted fluid that contained good and bad eggs into the uterus of a live mouse. The results were the same.
This study offers new hope for couples attempting to become pregnant through IVF and for women who suffer miscarriages.
Source: "The 'choosy uterus': new insight into why embryos don't implant." University of Southampton. 17 Sept 2013. Web. 29 Sept 2013.