There is a lot of planning and research that goes into gestational surrogacy. Many thoughts about surrogacy revolve around emotions and relationships such as the heartbreak of loss and the importance of trust and connection between the surrogate, the agency, and the intended parents. But one of the most important factors to understand is the science behind successful surrogacy. This includes the ability to produce embryos and test them for viability.
Accurate grading of embryos has become increasingly important over the years. When IVF technology was newer, multiple embryos were often placed in a woman’s uterus. The thinking is more settled, better are the chances of a successful pregnancy, which is to some extent true. Unfortunately, it also increases the likelihood of multiple births with all the inherent risks of miscarriage, premature birth, and defects.
The philosophy now is to carefully examine the embryos and select those that appear most viable for implantation. Here’s how it’s done.
Typically, embryos are scored at three days and at five days to determine if their development is progressing as expected and will be healthy enough to survive freezing or pregnancy.
Embryos are graded on a scale of one to four. Three-day-old embryos are called cleavage-stage embryos. Five days after fertilization, these are referred to as blastocysts. The three-day-old embryos are examined under a microscope to see if the cells are dividing as they should. They are graded based on the number and uniformity of the cells.
Normally, only those graded one or two will be placed. Sometimes grade three is used if other factors are made to appear viable or if grade one or two are not available.
At five days, the embryos are scored again, this time to ensure that the embryos continue to grow normally. Now they are graded from A to D. The “perfect” embryo would be rated 4AA, but there are many factors that go into determining quality and viability. Your reproductive endocrinologist will monitor them to assess which has the best chance of resulting in a successful pregnancy.
Accurate marking is important to both intended parents and surrogate pregnancies because they are both invested in a successful outcome. This topic is likely to be discussed at the contract stage when the parties agree on how many embryos are implanted and discuss a selective reduction. Embryo grading is actually an important aspect of the science behind successful gestational surrogacy. The grading process allows reproductive specialists to assess the quality and viability of embryos before implantation, increasing the chances of a successful pregnancy while minimizing the risks associated with multiple births.
Embryo grading usually occurs in two stages: three days after fertilization (cleavage-stage embryos) and five days after fertilization (blastocysts). Let’s review the scoring process at each stage:
Cleavage-stage embryos (graded on a scale of one to four): At the three-day mark, embryos are examined under a microscope to determine if they have undergone appropriate cell division. The number and uniformity of cells are taken into account in the scoring process. Generally, only embryos scored as one or two are selected for implantation. Grade three embryos may be used under certain circumstances, such as if other factors indicate viability or if grade one or two embryos are not available. Blastocysts (marked from A to D): On the fifth day, the embryos develop into blastocysts. At this stage, the marking becomes more nuanced, using a combination of two criteria: the expansion of the embryo (represented by a letter from A to D) and the quality of the inner cell mass and the trophectoderm (represented by the second letter from A to C). The perfect embryo, often referred to as “perfect,” will be graded as 4AA, indicating good expansion and quality. However, it is important to note that scoring involves various factors, and the specific scoring system may differ slightly between clinics or specialists. The reproductive endocrinologist closely monitors the embryos to determine which ones have the highest chance of resulting in a successful pregnancy.
Accurate marking is important for both intended parents and surrogate pregnancies as they share the common goal of a successful outcome. During the contract phase, discussions can take place about embryo transfer and the possibility of selective reduction (if multiple embryo implants). These conversations help establish mutual understanding and ensure that the parties involved are aligned with their expectations.
If you have additional questions about the science of embryo grading or any other aspect of gestational surrogacy, it is advisable to refer to previous posts or contact Surrogate Solutions or a reproductive specialist for more information.
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