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Understanding Embryo Grading

February 22, 2013

While there are many factors that play into the success of an in vitro fertilization (IVF) cycle, including uterine receptivity and hormone imbalance that could lead to pregnancy loss, perhaps the heaviest weight is placed on embryo quality. Approximately 60% of all miscarriages are the result of an abnormal embryo, but aside from biopsying the embryo via preimplantation genetic diagnosis (PGD), how can you tell if your embryo is of good quality?

Embryo Grading

Embryo grading is a process used by fertility doctors and embryologists to make an educated decision about which embryos have the greatest chance of developing into a healthy pregnancy. Michael Opsahl, M.D. of Poma Fertility in Seattle Washington says embryo grading is one of the ways fertility doctors and embryologists track the growth pattern of an embryo. “We think of embryos as having a story. There are several things we look at when grading embryos including the changes that occur at certain periods. If [the embryo] does not follow a normal progression, that is an indication that it is not a good embryo,” he says. Embryos are graded on visual characteristics including cell size, clarity, fragmentation, how grainy the embryo appears, and number of cells. “The two most common criteria for grading an embryo are number of cells and fragmentation. When cells die, they fragment, so that is evidence that they are not as healthy,” says Opsahl.

Looking at the Big Picture of Embryo Development

Klaus Wiemer, PhD, HCLD, ACE, Embryologist at Poma Fertility agrees that embryos are a dynamic entity. “If we only use the data at the end point of a blastocyst development, we don’t have a good idea of the actual quality of the embryo,” he says. Embryos that appear to be high quality on one day may not demonstrate the same high quality the next day. Therefore, it is important to take a detailed report of the embryo growth pattern each day leading up to embryo transfer. Embryologists should also monitor the rate of growth, as embryos that grow too fast or too slow show higher rates of aneuploidy- an abnormal number of chromosomes.

“Normal embryos tend to double in cell quantity each day. On day two or day three, if you have a 4 cell embryo there is a 70% chance it will develop into a high quality embryo,” states Wiemer. A fertility patient might receive an embryology report that indicates both number and letter grade for each embryo. The number indicates how many cells are present in the embryo. The first letter details the condition of the inner cell mass of the embryo (becomes the fetus), and the second letter tells the embryologist about the quality of the trophoderm, or outer layer (becomes the placenta). Typically embryos are graded as follows:

  • Grade A is good quality
  • Grade B is medium quality
  • Grade C is poor quality

“If we have three blastocysts and all three look the same, we would then rely on the history to determine which embryo we should transfer,” Wiemer explains.

Fertility doctors then take the embryo grade and compare it to the patient’s age, diagnosis, and outcome of previous cycles to determine how best to proceed at time of embryo transfer.

Embryo Grade and Pregnancy Outcomes

Fertility doctors and embryologists use embryo grading as an important tool to help patients have a successful IVF cycle or to understand what might have caused a cycle to fail. Both Opsahl and Wiemer believe that having an open discussion with patients and providing a detailed embryo growth history is key making decisions about future fertility treatments as a team.


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