What are the recent developments in implantation? (Part One: Embryo quality)

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This post is part one of a series where we will discuss how embryos, the uterus and overall health impact implantation.


For many years in fertility care, we were only able to guess why some people weren’t able to achieve pregnancy. When running IVF, we would grade embryos, a technique that is presumed to predict the likelihood of ongoing growth and development.

But when an apparently good embryo wouldn’t stick, we didn’t have a specific explanation as to why.

Increasingly, we are now able to identify the issues.

Most implantation failures are related to embryo quality. So let’s start there. It turns out that 93% of the time recurrent pregnancy loss is related to abnormal embryos, 90% of which comes from egg-quality concerns.

There are three ways that we judge embryo quality.

We judge embryo quality in three ways: the number of embryos present, embryo grading, and PGS. In this post, we’ll talk about the number of embryos present.

We know from pre-implantation genetic screening (PGS) data generated by Dr. Munne, that the greater number of blastocysts that are present, the more likely any individual blastocyst is healthy. This has been well demonstrated at our clinic.

When women under 35 were looking to transfer two embryos, but there are only two present to begin with, the chances for pregnancy are approximately 44%. If there are three or more – that is, we can choose to transfer two and freeze the remainder – the pregnancy on the fresh transfer will be 70%.

Similar ratios hold true for all age groups. For example, in women over 40, the pregnancy rate is four times higher if there are three or more blastocysts, with the transfer of two, versus only two present.

The higher the number of available embryos, the more likely any individual embryo will be genetically normal. This statement is true to a point: There are no great advantages, and possibly some disadvantages, in hyperstimulation and generating too many embryos.


Note: Embryos are just one element in implantation. Implantation challenges can be related to embryos, the uterus and overall health. We’ll have another post shortly on how the uterus, its shape and lining, may impact odds for implantation.

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