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Embryology terminology – technical terms you should be aware of

Carolina Andrés
Embryologist, Andrology Laboratory at Clinica Tambre, Clinica Tambre

IVF laboratory

From this video you will find out:
  • What is a karyotype, and what is it used for?
  • What terminologies are used for semen analysis?
  • What is the meaning of sperm DNA fragmentation (SDF)?
  • What is the structure and stages of mature oocytes’ development?
  • How do you assess ovarian reserve?
  • How is IVF done—step by step?
  • What are the 4 stages of embryonic development?
  • How do you evaluate the quality of embryos?
  • What is the PGT procedure, and how is it done?
  • How do you read PGT results?

What embryology terms you need to know during your fertility treatment?

In this webinar, Carolina Andrés, Embryologist, Andrology Laboratory at Clinica Tambre talked about technical terms in embryology that you need to be aware of.

What embryology terms you need to know during your fertility treatment? - Questions and Answers

What are your thoughts on refreezing already thawed embryos?

It’s something that we do at the laboratory in some cases, for instance, we have some embryos are frozen, which we have not analysed genetically, and at some point, we want to analyse them. We would do the thawing procedure and then the freezing, and we can do it without any problems. Indeed, it wouldn’t be our first choice, it would be better to do the genetic analysis before, but we still can do it without any problems.

Is it true, embryos stop growing after day -3 because of the sperm factor?

It’s true that when we see that embryos stop growing more at day-4 or 5, we would say that it’s a more male factor. However, it is important to analyse each case specifically. As I said, each case is different, and it’s important to analyse all aspects, but talking in biological terms, it’s normally associated with a male factor.  As I said, we must be careful and analyse the whole case.

Which grade embryos should be transferred first?

Our indication would be to transfer embryos that are AA, which is like the top quality. Then we would consider transferring embryos which are, for example, BA. At our clinic, we prioritize the trophectoderm quality, but as I said, each clinic has its protocol, at our clinic, we would first transfer blastocyst AA.

Can mosaic embryos correct themselves, and when do you transfer such embryos?

Mosaicism is something that we are starting to see better because of the advances in PGT technology. It is important to know that when we do the PGT, we analyse cells from the trophectoderm, so we don’t know if the aneuploidies will be in the whole part of the embryo, or just in the trophectoderm, therefore it’s a question that’s very difficult to answer.

Most mosaic embryos can be transferred, it’s something that the genetic laboratory can give you the indications for transferring such embryos and inform you about all the risks. These embryos would be transferred only after all the euploid embryos are being transferred. 

What will be the next choice for embryo transfer, after 5 AA blastocyst?

We would choose the more expanded embryo. We have to take into account different factors. For us, it’s more important to check the quality, so embryos with the best quality are with letters A and B. At our clinic, we do not transfer embryos letters C or D in any of their parts. First, embryos AA would be transferred, for example, as you said, 5AA blastocyst.

Later, we would transfer, for example, BA. We would prioritize the trophectoderm quality, which is better than the inner cell mass, so we would choose BA and then maybe we would choose a blastocyst A in the inner cell and B in the trophectoderm. Finally, a blastocyst BB, as I said, the most important thing you must know from this is that a blastocyst with these letters is of very good quality, both letters A and B are very good quality blastocysts. 

Do you often do transfers with mosaic embryos at your clinic?

We’ve transferred mosaic embryos, I haven’t had many cases because normally, as I said, we prioritize transferring euploid embryos, which have a higher implantation rate. I cannot tell you a number since I don’t know, but we have transferred mosaic embryos that have developed into a healthy pregnancy.

To clarify 5AA, 5BA, 5 AB and then 5 BB, correct?

Yes, at least at our clinic, we would choose them like that. 

Carolina Andrés

Carolina Andrés

Carolina Andrés is an Embryologist at Clinica Tambre, Madrid, since 2017. Carolina graduated in Health Biology at the University of Alcalá de Henares in 2015. She obtained her Master's Degree in Human Reproduction from the Complutense University of Madrid and the Spanish Fertility Society in 2016. In 2017, she also obtained a Master's Degree in Cytogenetics and Reproduction Biology from the Autonomous University of Barcelona. She speaks Spanish, English and French.
Event Moderator
Caroline Kulczycka

Caroline Kulczycka

Caroline Kulczycka is managing MyIVFAnswers.com and has been hosting IVFWEBINARS dedicated to patients struggling with infertility since 2020. She's highly motivated and believes that educating patients so that they can make informed decisions is essential in their IVF journey. In the past, she has been working as an International Patient Coordinator, where she was helping and directing patients on their right path. She also worked in the tourism industry, and dealt with international customers on a daily basis, including working abroad. In her free time, you’ll find her travelling, biking, learning new things, or spending time outdoors.
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