Achieving a healthy baby is the goal. You have now found yourself at the threshold of the fertility clinic and are trying to decide whether to add PGS (pre-implantation genetic screening or comprehensive chromosome screening) to your treatment plan. And if you do, what day will your embryos be biopsied? And is it ok to freeze the embryos? These and other questions are important considerations and require some discussion.
To PGS or not to PGS?
There are several reasons to undergo PGS. In our clinic, we recommend considering PGS for the following circumstances:
- Patients with a genetic disease or carriers of a genetic disease who wish to avoid passing onto a child.
- Patients that have had prior miscarriages (2 or more) and especially if the miscarriage was due to an aneuploid fetus (chromosomal abnormality).
- Patients that have had 4 or more excellent quality blastocysts transferred through IVF but have not conceived, especially if they still have 4+ frozen embryos or are contemplating a new cycle.
- Patients that are over 38 years old that wish to decrease their miscarriage rate, decrease their chance of having a child with a chromosomal abnormality and increase their chance to have a successful pregnancy from IVF.
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Because of the time and emotional toll a miscarriage engenders, taking an extra month to biopsy the embryos may make sense, especially for older women who have less time on their fertility clock. In addition, because a frozen embryo transfer (with 1-2 embryos) costs around $4k and PGS costs around $6k, using PGS to identify the best embryos for transfer may provide a cost savings for the patient rather than repeated frozen transfers.
Which day will the embryologists biopsy my embryos?
Embryo biopsy can be done on the polar bodies on day 0 to 1, on cleavage stage embryos on day 3, or at the trophectoderm stage on day 5/6.
Polar body biopsy provides only limited data as the embryo can still undergo genetic changes.
Cleavage stage biopsy has been shown in a recent study by Scott, et al (2013) to decrease implantation rates of a normal embryo from 50% to 30%.
Trophectoderm biopsy on day 5 or 6 is the most likely to give a true read of the embryo’s genetic make-up and allows for several cells to be sampled to strengthen results, and causes no (or less) harm to the embryo.
At RSC, we biopsy on day 5 or 6 or whenever the embryo has developed enough to allow a safe and simple biopsy (usually a grade 3BB or better embryo.)
Fresh or frozen transfer?
A fresh embryo transfer after biopsy allows for a quicker pregnancy result. However, since the testing of the embryo takes time (at least 24 hours at RSC) the embryo would have to be transferred on day 6 or 7. We feel success rates are not as good with a fresh transfer on day 5 as they are on day 6 to 7, so we choose to vitrify the embryos while we wait for the results, thus putting the embryo back into the uterus in a frozen cycle.
As the speed of the PGS technology increases, we may be able to transfer the embryo back in a fresh cycle, but there are already concerns that the endometrium in a fresh cycle is not as good as in a frozen cycle. Several studies support the fact that the endometrial-embryo relationship is optimized in a frozen programmed cycle when high dose gonadotropins are not used. This may account for the healthier placentas and healthier babies born from a frozen cycle.
All of these decision points may seem overwhelming at first, but rest assured that we at RSC will help you sort through the issues and make good decisions with sound medical advice during each step of your fertility journey.