By: Charis Johnson

There are many factors to consider when matching with a set of frozen embryos. Which factors are the most important? Which embryos have the best chance of becoming a take-home baby? While each embryo is precious and the answers to these questions will be different for each recipient family, there is scientific information you can utilize in your decision-making process. Knowing frozen embryo criteria is key.

Many families have preferences on variables such as race, eye/hair color, height, and educational background of donors. If you have selected a Closed or Anonymous adoption, variables concerning the embryo’s health and likelihood of pregnancy will be important to you. In addition to these, variables concerning the embryo donor family will be important to those who have selected an Open or Semi-Open adoption. These could include a donor’s location, religious beliefs, expected level of communication, and philosophy on embryo adoption. When considering a set of embryos, it is important to understand the variables surrounding the donor’s maternal age, history of infertility, length of time frozen, and embryo grading.

Maternal Age of Donor

A broadly accepted generalization is that the older the maternal age of the donor, the lower the chance of an embryo becoming a take-home baby. Because of this, the older the maternal embryo donor is, the more embryos a doctor will allow to be thawed at one time. The following guidelines are recommended for fresh frozen embryo transfers by SART. One additional embryo may be transferred if the donors/recipients have experienced a history of failed transfers or have a less favorable prognosis.

MATERNAL AGE OF EGG DONOR: Less than 35 35-37 38-40 41+
Favorable Cleavage Embryos (Day 2-3) 1-2 2 3 5
All Other Cleavage Embryos (Day 2-3) 2 3 4 5
Favorable Blastocysts Embryos (Day 5-6) 1 2 2 3
All Other Blastocysts Embryos (Day 5-6) 2 2 3 3

Fertility of Donors

To determine the fertility of your donors, consider asking the following questions:

  • Were the embryo donors successful on their first round of IVF?
  • Were they were successful in achieving pregnancy on every round of IVF they completed?
  • Were the embryos remaining from IVF cycles were good enough quality to freeze?
  • Have frozen embryos achieved pregnancy from this IVF batch?

The more questions they can answer yes, the greater your odds of matching with healthy embryos. Please note that the variable in this equation is always the recipient’s ability to receive implantation and carry to term.

Length of Time Frozen

The length of time the embryos have been frozen has no impact on the viability of the embryos. Frozen embryos never expire or get “freezer burn”. This does not, however, mean that they are “safe” in their frozen state. Human error including broken vials, transferring the wrong embryos, or power loss could destroy the embryos. While the length of time the embryos have been frozen has no impact on their viability once thawed, the method that they were frozen with does. “Slow freeze” embryos have a slightly lower rate of survival than embryos that were frozen using the more recent “vitrification” process.

Four-cell embryo , 3d illustration

Embryo Grading

Day 5 “Blastocysts” Embryos

Many clinics use different grading systems to score the frozen embryos. It is important to read the embryology report to determine how their grading system works. The commonly used Gardner blastocyst grading system assigns 3 separate quality scores to each blastocyst embryo.

For example, if an embryo is graded a “5AB”: “5”: describes the Blastocyst development stage. This number describes the progress the embryo has made towards expansion and hatching. The goal is for the embryo to be a “6” so that it can easily implant, however, the embryo can continue to expand and hatch in the uterus after a transfer.

Expansion grade Blastocyst development and stage status
1 Blastocoel cavity less than half the volume of the embryo
2 Blastocoel cavity more than half the volume of the embryo
3 Full blastocyst, cavity completely filling the embryo
4 Expanded blastocyst, cavity larger than the embryo, with thinning of the shell
5 Hatching out of the shell
6 Hatched out of the shell

The letter “A”: describes the status of the Inner cell mass (ICM) score, or quality. This is the part of the embryo that will become the baby. Just like a school grading system, an “A” is considered more preferable to a “C”.

ICM grade Inner cell mass quality
A Many cells, tightly packed
B Several cells, loosely grouped
C Very few cells

The letter “B”: describes the status of the Trophectoderm (TE) score, or quality. This describes the appearance of the cells on the perimeter of the embryo.

Day 3 “Cleavage” Embryos

There are many embryo grading systems that differ in how they assign grades and in whether a low number grade indicates the best or the worst embryo. It is important to clarify what scoring system was used when they were originally evaluated. Day 3 embryos are graded based upon their appearance.

  • Cell number (are they growing?) Embryos should be at 2 to 4 cells at 48 hours after egg retrieval and preferably about 7 to 10 cells by 72 hours. The cells in an embryo are also referred to as “blastomeres”.
  • Cell Regularity (are the cells the same size?) Generally speaking, the more identical the cells are to one another – the better.
  • Degree of Fragmentation (are pieces chipping off the cells?) Fragmentation occurs when portions of the embryo’s cells break off. It is preferable to have little or no fragmentation; however, it is quite common, and many beautiful babies have resulted from implantation of embryos with fragments. Embryos with more than 25 percent fragmentation are said to have a low implantation potential.

 Special Consideration Embryos These embryos have extenuating circumstances that need to be considered in the selection process. Sometimes single embryos are placed in this category because they are more difficult to find a family for. Oftentimes there has been an instance of genetic abnormality, special need, miscarriage, or birth defect in a biologically related sibling.

Blog written by Charis Johnson, co-founder of NRFA.