Useful embryo pictures for both patients and embryologists

February 11, 2013Carole 1 Comment »

Sometimes a picture really is worth a thousand words, especially when you want to understand the microscopic world of embryology. The European Society of Human Reproduction and Embryology (ESHRE) recently published the Atlas of Human Oocytes and Embryos and have made it available for free on-line in either HTML or PDF form.

Click on the chapter links below to go to each on-line chapter with pictures.

Chapter One: The Oocyte Whether you are a patient trying to understand your embryology report or a embryologist trying to understand the basics of embryology development, this chapter is a useful primer for better understanding the human oocyte. Did you know that oocyte maturity is reached when BOTH the nucleus and the cytoplasm become mature and that sometimes, in gonadotropin stimulated cycles, these two types of maturity may not be well synched?  At retrieval, the presence of a polar body is routinely used to indicate that the egg reached nuclear maturity but that may not be sufficient. The postponement of ICSI or insemination for a few hours may be beneficial to allow lagging areas of egg development to catch up. You can see photos  of cumulus-enclosed oocytes and denuded oocytes with various features such as polar bodies (excess cytoplasmic and genetic “baggage”), the perivitelline space (space between the egg and the shell) and the  zona pellucida (the shell), This section discusses both normal variation in egg appearance and other abnormal, potentially lethal characteristics such as aggregations of smooth endoplasmic reticulum or giant oocytes (containing multiple genome sets). You can find pictures of eggs with a prominent germinal vesicle, a structure that exists in the immature egg, but disappears (germinal vesicle break down) with egg maturation.  You’ll see eggs with grainy or clear cytoplasm, cytoplasm containing vacuoles or refractile bodies and cytoplasmic areas of clustered organelles. For patients, these photos can be used as a glossary to decipher terms your embryologist throws at you. For the embryologist, these photos are useful standards to compare with your everyday observations of embryos in the lab.

Chapter Two:  The Zygote You may have asked yourself, “What the heck is this “two pee N”, that my embryologist is rambling on about?” A “2PN” is short hand for the number of pronuclei in the egg after it is fertilized. A fertilized egg briefly exhibits two pronuclei (one from mom and one from dad), before these dissolve and the embryo continues on as a new genetic organism. You can see many pictures of normal 2PN, as well as abnormal PN (multiple PNs such as 3PN, 4 PN etc.) zygotes What’s nice about the descriptions for the photos is that in many cases, there is information about whether these features resulted in a viable embryo or not, or whether it was transferred and sometimes whether the patient became pregnant.  Zygote scoring, one system of embryo evaluation,  is described in detail with these photos. Some programs, but certainly not all, have identified desirable characteristics of pronuclear alignment and size that they believe are useful in identifying those embryos most likely to implant. Whether these scoring systems really make a difference is not clear but embryologists are always trying to find better markers for embryo selection and zygote scoring is one such system. Particularly if your clinic uses this approach, it may help you understand what they are looking for in the embryos they prefer to transfer.

Chapter Three: The Cleavage Stage Embryo

In this chapter, you can learn more about what embryologists expect from your embryo as it develops. You can see what your embryo looks like as a “two-cell”, “four-cell” or “eight-cell” embryo.  Your embryologist may talk to you about seeing fragmentation in your embryos  or other cytoplasmic abnormalities. You can look at embryos with 15%, 25% or 40% fragmentation to give you an idea of what this looks like.   You can also look at diagrams that explain what normal development looks like, when cells divide in an organized fashion vs. unregulated chaotic generation of various sized daughter cells. Examples of embryos with various numbers of cell nuclei are shown and the implications for normal development and pregnancy are discussed. A cell should only have one nucleus, except if it is on the verge of dividing, then two might be okay. Multi-nucleated cells of higher order are always abnormal and embryos with these features are usually excluded from transfer. As the embryo develops, it transforms from a collection of loose cells to an interconnected entity, and the spatial orientation of cells within the embryo become increasingly important. As cells start to respond to internal signals of spatial orientation, cells start to “smoosh” together into a morula, the stage between the cleavage stage embryo and the blastocyst. Although scoring systems don’t really exist for the unattractive interim morula stage embryo, embryologists like to see that all of the embryo’s cells are included in the “smooshing” process.

Chapter Four: The Blastocyst

With the formation of a blastocyst, the embryo’s cells have taken on specific duties such as contributing to the cell lineages that become either the fetus itself or the fetal part of the placenta.  Your embryologist will describe your blastocyst by talking about its degree of expansion (partial or fully expanded) and the effect of this expansion on other structures of the embryo (eg. the zona pellucida thins and the perivitelline space disappears while a fluid-filled space (blastocoel) forms inside the embryo. You can see pictures of embryos with stages of blastocoel formation described by how much of the embryo’s volume is taken up by this space. Your embryologist may have spoken of a cytoplasmic string or bridge between the intracellular mass (the ICM= future fetal cells) and the trophectoderm cells (TE= future placenta cells). There are pictures of embryos with two, instead of one ICM, which is one cause of identical twins. There are pictures of embryos with dark cells, indicating that some cells have degenerated in the blastocyst which does not bode well for implantation.

If you are a patient, you’ll probably find out everything you need to know by reading the captions with each photo. If you are an embryologist, you’ll probably want to dig deeper into the text. If you are a teacher, you can download power point slides of  photos to share with your students. If you simply like looking at pretty (or weird)  pictures of eggs and embryos, you’ll enjoy this atlas too.


© 2013, Carole. All rights reserved.

One response to this entry

  • Texasanfe Says:

    Thank you so much or posting. We can only learn by seeing and understanding current embryonic situations, by example.

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