People are born into a lifetime of exams. Exams start at the moment of our birth and continue throughout our lives. We face medical exams, final exams, drivers' license exams, professional exams, and even job interviews are exams of a sort. Recently, in an examination of the reproductive process, medical researchers in England discovered that we must pass the most important exam of all long before our birth. When we are nothing more than microscopic embryos, we must pass an entrance exam or the uterus will not allow us to implant ourselves in its lining.

How implantation works

This news is especially exciting for infertile couples and the medical community that works with them. In its most fundamental description, in vitro fertilization (IVF) involves an egg fertilized in a lab where it’s coaxed to become an embryo. This embryo is then implanted in the womb of the woman, with the hope pregnancy will develop and a baby will be born.

Not every embryo implanted turns into a pregnancy, though, and success is usually unpredictable. In about 15% of implants that become recognizable pregnancies, chromosomal abnormalities and uterine stress responses to the embryo result in miscarriage. Implant failure is the leading cause of unsuccessful treatment although the reason why this happens, exactly, has been somewhat elusive.

The medical research team examining the issue was based at the Warwick Medical School and involved reproductive scientists from across England. They were working on the knowledge that, like snowflakes, no two human embryos are the same. Each one is highly diverse genetically before implantation and its health, or viability, varies accordingly.

Which embryos implant more?

In some embryos, there are no normal cells at all but others contain some healthy cells and some that are damaged. Others are entirely viable. The Warwick study indicates that only those of high quality are allowed to implant.

The Warwick researchers discovered that embryos of high genetic quality secrete trypsin, a chemical that signals the lining of the uterus to prepare for implantation. Poor quality embryos do not send this chemical signal so the womb does not prepare for implantation. Poor quality embryos actually trigger an alarm response in the uterus which often means the death of the faulty embryo.

During IVF, each embryo is assessed for its life-giving potential and only those that show promise are implanted. Since it is now evident that the lining of the womb also plays a decisive role in the womb’s acceptance of the implanted embryo, the research team expects an examination of tissue samples of the uterine lining to become a part of the IVF process.

There is speculation that a greater understanding of the receptivity of the uterine lining will lead to corrective measures that better prepare the womb for implantation and a greater rate of IVF success.

Source: “The ‘entrance exam’ that is key to a successful pregnancy (press release).” Warwick News & Events. The University of Warwick. Feb 6, 2014. Web. Feb 14, 2014.