Preimplantation Genetic Diagnosis

Today we shared some sad news during our medical session. One of the cases we commented was Sandra P.’s.

Sandra and Pedro came to our centre after 3 years of sterility due to a blockage in her fallopian tubes. They had undergone two In Vitro Fertilisation cycles at another centre and had had no success.

Before going on with a new treatment, we decided to have some tests done first, including a basal hormone analysis. These are performed on the second or third day of the menstrual cycle and they show the patient’s ovarian age. You must know that, sometimes, our biological age doesn’t correspond with the age of our ovaries, there’s usually a three years different between both approximately.

Well, while Sandra was 38 at the time, her ovaries appeared to be 40 years old. We suggested it would be convenient to analyze the chromosomes in the embryos, and they agreed. During the cycle we obtained 7 oocytes, and IVF was performed on the 5 most mature oocytes, 3 of which fertilised. Three days after fertilisation, two embryos had evolved. We planned to analyse both embryos genetically on that same day, but in the end the couple decided not to. They preferred to have the transfer on that very day as, being only two, they thought it was useless to choose the best, and, additionally, they would save the cost of the analysis.

Sandra became pregnant. That same week, though, we diagnosed her embryos Down Syndrome during the amniocentesis test and her pregnancy was interrupted.

Reaching this circumstance is sad, as we had the opportunity to prevent such an unfortunate situation by means of Preimplantation Genetic Diagnosis.

Let me show you how it’s done…

See… all cells are equal in a 3 day old embryo. We can extract one and analyse it and it will be regenerated in a few hours (like a lizard’s tail)… It seems science fiction but we can actually know an embryo’s karyotype (the map of its chromosomes) in 48 hours.

What is Preimplantation Genetic Diagnosis?

According to studies conducted in our centre, in the best of cases, ie using embryos from donor sperm and oocytes, almost half of them show chromosomal abnormalities. It seems a lot, but truth is human reproduction is quite ineffective: in an egg donation cycle we usually transfer two embryos hoping one will implant.

The percentage of abnormal embryos increases accordingly to the woman’s age, so 78% of the embryos of 40 year old patients are altered. In short, most of these embryos either do not lead to pregnancy or lead to spontaneous miscarriage.

Percentage of embryos with abnormalities in cycles for patients using normal sperm without previous miscarriages:

Women aged 35-37: 70.6%

Women aged 38-41: 78%

Women aged 42-43: 92%

Preimplantation Genetic Diagnosis allows us to transfer embryos that, besides looking physically good, don’t display abnormalities. The technique isn’t used systematically because it’s still quite expensive and not all centres can perform it, though centres who do not offer it can send the cell to another centre for it to be analysed.

Daily, we study many cells from embryos who lie in incubators in other centres, some of which are very far away. The cell arrives and, before 48 hours go by, the results are sent by mail and the healthy embryos are transferred fresh 2 days later, 5 days after IVF.

It has happened that in some cycles all embryos show abnormalities and cannot be transferred. This has even been the case for patients for whom we’ve analysed up to 10 embryos! If these hadn’t been examined, the patient would have had 2 or 3 fresh embryos transferred, she would have frozen the 7 remaining embryos and would have undergone 2 or 3 more cycles with these… including everything it entails: hope, money, travel, absence at work, etc.

Preimplantation Genetic Diagnosis allows us to select the chromosomally normal embryos. Hence, we increase the chances of pregnancy and decrease the risk of a spontaneous miscarriage or finding a problem we could’ve prevented during an amniocentesis test, like in Sandra P.’s case.

1 Comment

  1. Dharshi Reply

    Did PGs and transferred one embryo. Now at 12dp5dt my hcg is around 900. Should I be worried?

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