Embryo Morphology serving Dallas, Frisco and the North Texas area

Embryologists use several criteria to determine the health of an embryo and one parameter is embryo morphology. Selection of the “best” embryo, that is, the embryo that is most likely to implant and establish the pregnancy, is based on a number of parameters. This section of the web site is a review of embryo morphology showing examples of embryos that have resulted in pregnancies in the IVF laboratory.

Day 0

Picture of oocytes (eggs) harvested following the oocyte retrieval procedure. The oocytes (A) are surrounded by a mass of cumulus cells (B), which are intimately associated with the oocytes and play an important role in the nutrition and maturation of the oocytes during follicular development in the ovaries prior to ovulation.

Picture of a mature oocyte following removal of the cumulus cells. The main characteristic of a mature oocyte is the appearance of a round structure (at 12 o clock in the picture) known as the first polar body. The oocyte is one of the largest cells with an approximate diameter of around 100-120 µm surrounded by a gelatinous shell called the zona pellucida. The oocyte carries the 23 maternal chromosomes for procreation.

Day 1

Picture of a fertilized oocyte or 2PN (pronuclei) observed in the morning of the day after the oocyte retrieval procedure or 17-19 hours following insemination (IVF) or sperm injection (ICSI). The two circular structures observed in the middle of the oocyte are called pronuclei, which contain the genetic material from the parents. A normally fertilized oocyte should have two of these structures one derived from the sperm (paternal) and the other from the oocyte (maternal).

Picture of a group of normally fertilized oocytes showing the 2PN structures.

Picture of a fertilized embryo undergoing the first cell division 25 hours after insemination (Late Day 1).

Day 2

Picture of a 4-cell embryo on day 2 of in vitro development. The embryo has gone through two divisions and has four evenly sized cells.

Day 3

Below is a picture of an 8-cell on day 3 of in-vitro development. Embryos should have between 7-10 cells. Embryos with low number of cells, uneven sized or irregular appearing cells and a high degree of fragmentation have a lower chance of implanting than do embryos with higher cell numbers, evenly sized cells and <5% fragmentation.

Embryos with higher cell numbers, regular appearing cells and little or no fragmentation have a higher overall chance of implanting than do other embryos with less cells, more irregularity and significant fragmentation.

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. Our embryologist use a grading criteria to determine which is the best quality embryos for transfer. If you have embryos that meet criteria for crypreservation, then you will be offered a single embryo transfer.

Grading Embryos

The following parameters are used to evaluate embryos at the world class laboratory of Fertility Specialists of Texas.

Cell number

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 refered to as "blastomeres".

Cell regularity - degree of regularity of size of blastomeres

It is generally best if the size of the individual cells (referred to as blastomeres) in the embryos are similar in size. If they are not, it is better if they are close to the same size, as compared to very different in size.

Degree of fragmentation

Fragmentation is a process where portions of the embryo's cells have broken off and are now separate from the nucleated portion of the cell. It is preferable to have little or no fragmentation.

However, fragmentation in human embryos is quite common and many beautiful babies have resulted from implantation of embryos with fragments potential.

Presence of multinucleation

An embryo is multinucleated if more than one nucleus can be seen in any individual cell on either day 2 or day 3. After day 3 it is extremely difficult to identify the presence of multinucleation. The majority of multinucleated embryos have been shown to be chromosomally abnormal in PGD studies.

However, sometimes multinucleated embryos implant and lead to a healthy pregnancy and birth of a normal baby. These embryos are generally only transferred to the uterus if they are the only ones available.

Day 4

A Morula is a compacted embryo composed of several blastomeres.

Day 5

When blastocysts are evaluated and graded (see picture below), emphasis is placed on the inner cell mass (baby cells) size, cell number, compaction and overall appearance. This is going to form the baby and is the most important criterion for blastocyst selection.

Secondary, the trophoblast cells (cells forming the placenta) are evaluated for number, equality of size and distribution.

Blastocyst developmental stage is also evaluated with a more advanced degree of expansion preferred.