Ask an Expert: Embryologist Part Three, Genetic Testing

Ask an Expert addresses reader questions every week. Today we share expert insight from Kristen, an Embryologist who will answer a few of your top genetic testing questions. Stay tuned for future posts, as this is part three of the embryology series.  

Why would a PGS tested embryo miscarry?  

Issues with the uterus such as polyps, fibroids, adhesions, endometrial inflammation can all interfere with early pregnancy.  

Issues with the embryo. 

Small mutations not detected with PGS. 

The metabolism of the embryo and how the genes function/malfunction. 

Mosaicism – the embryo testing is limited to the cells used and it may test as normal but the embryo is actually abnormal. 

The trophectoderm may be good enough to implant but not good enough to continue the process of creating the vasculature of the placenta. 

Why would genetically normal embryos not implant? 

Issues with uterus and embryo as above. 

The endometrium is not as receptive as it should be. Good progesterone levels and a good endometrial thickness is needed for this. 

Issues with the procedure. E.g. Difficult embryo transfer procedure can cause contractions of the uterus and/or a difficult anatomy can make the transfer more complicated. 

Is embryo genetic testing worth the money? 

Not everyone needs to have genetic testing. I believe the studies are now showing it’s not recommended as the risk to the embryo doesn’t justify the benefits, HOWEVER, for the subset of patients that are of advanced maternal age and thus at much higher risk of abnormal embryos, it’s absolutely worth it as the time to pregnancy is much quicker, and the chance of miscarriage is lower. For those who have had multiple miscarriage or need to test for genetic disease, then yes, it’s absolutely worth it. For younger patients with lots of embryos it can reduce time to pregnancy by reducing the number of transfers needed via excluding the abnormal ones.  

Do PGS tested embryos have greater success rates? 

Yes, a PGS normal should have about double the success rate of a non-tested embryo, for younger patients it’s much higher than double.

Should all embryos be sent for genetic testing? Our clinic charges per embryo. 

If you have many embryos, having them tested will likely change the order in which they will be used as compared to choosing an embryo based on morphology (physical quality), so time to pregnancy will be sooner. If money is an issue you could test the few best quality ones but obviously there is a chance none will be found normal and the selection of the embryos for testing can be quite difficult. This is referring to the patients that for various reasons have decided along with their clinician to have genetic testing. I do not say that all embryos for all patients should be tested. 

If an embryo is genetically abnormal, do we still have the option to transfer it? In which case would you recommend transferring an ‘imperfect’ embryo? 

This depends on what is wrong with the embryo. In some situations of ‘mosaic’ embryos (where some cells are normal and some are abnormal), you may be able to have it transferred if it comes back as ‘low risk’, although you may need to see a genetic counselor first. In ‘complex abnormality’ embryos, these cannot be transferred as well as embryos that have whole or partial chromosome duplication’s or deletions.  

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Kristen has been an Embryologist for 5 and a half years. She studied Biomedical Science and has a Master’s degree in Reproductive Medicine. She’s always had a passion for fertility and a desire to help others going through such a hard and emotional journey. 

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