Embryology 101

Look, I’m no expert, but I had to make myself understand a few things, so here goes, hope you can take something away from this.

Making heads from tails from my own embryology was a bit of a challenge, simply because I’m no embryologist, but I wanted to understand what’s going on there, so I started googling extensively, as one does under these types of circumstances.

The first thing I realised is that not all oocytes are mature at retrieval, apparently, according to studies it’s acceptable for 25% to be immature.

So what are the different stages of Oocyte development? Below you can see a diagramatic model of Oocyte development which I got from The Handbook of the Assisted Reproduction Laboratory. (Would love to own that book by the way!  But the price, as expected of such a specialist book, is a little prohibitive, the preview did come in handy though) Anyhow, let’s move on.

As you can see, during Prophase I the Germinal Vesicle is clearly visible.

Enter Metaphase I, there is no Germinal vesicle visible and also no polar body.

Metaphase II is the exciting part, this is where we want to be as close as possible to retrieval, because the oocyte needs some ingredients in the follicle to mature optimally.  Here we can clearly see an extruded polar body, which indicates that the Oocyte is ready fo insemination.  The Oocyte “divides” in two, creating a primary (the oocyte that fertilises) and secondary oocyte (the polar body).  The polar body in the perivitelline space contains a duplicate copy of the primary oocyte’s DNA, and it’s this little bugger which they use to perform Array CGH to screen oocytes for viability.

During the next phase, after successful fertilisation one can clearly notice two polar bodies and two pro nuclei.  The pronuclei are only visible for a brief window, so don;t panic if you can;t see this on your embryology.  It simply means the picture was taken outside this critical window.

From here cleavage takes place. You can read more about that here.

If you’d like to read some more interesting articles on oocyte/embryo development, have a squiz here:

http://www.embryo.chronolab.com/index.htm

http://ivf.net/ivf/embryo_development-o2591.html

http://fertilicare.org/faqbase/?p=773

http://infertilityblog.blogspot.com/2009/04/meet-blastocyst.html

And that’s about as much as you need to know about Embryology 101, enjoy!