Once eggs have been collected from the in vitro fertilization procedure, they must be fertilized with sperm. Sperm from a woman’s spouse, partner, or donor sperm can be used. There are two types of fertilization procedures; conventional fertilization and intracytoplasmic sperm injection (ICSI).
Just after the egg collection or retrieval procedure, the eggs still have a mass of cells around them called cumulus cells. These cells provide support to the egg during the development and maturation process. These cells will obscure the egg from view which makes it more difficult to determine if the egg is of good quality. Having good quality eggs is very critical to the overall success of the IVF process, and poor quality eggs is a major cause of infertility.
Collection of the Eggs
The eggs are collected during the oocyte retrieval procedure. The embryologist receives the eggs in a test tube that has media designed to protect the eggs from chemical and environmental harm. These test tubes are emptied into petri dishes where the individual eggs can be identified. The embryologist uses a high-magnification microscope to identify the eggs. As the eggs are found, they are moved into a dish used to collect the eggs together. These dishes are labeled and color coded to protect the identity of the parents. After all of the eggs have been collected and identified, they are placed into the incubator for the fertilization procedure. If there are problems with the sperm count, motility, or morphology (shape) of the sperm, ICSI is used to inject sperm into the egg. When the sperm counts are normal, and male infertility is not suspected, the sperm can be placed in the dish with the eggs. The day of fertilization is considered day 0 when discussing embryos and embryo transfer procedures.
Conventional Insemination – IVF
With normal sperm counts, sperm undergo a preparation technique often referred to as washing, or simply a “sperm prep” procedure. This processing is designed to help isolate motile sperm that can be used to fertilize the eggs. After the washing process, approximately 50,000 motile sperm are placed with each egg. The egg still has the outer cluster of granulosa cells which act as a natural barrier to the sperm. The sperm that eventually fertilizes the egg must pass through these outer cells and through the thick wall surrounding the egg known as the zona pellucida. Once one sperm enters the egg, the zona pellucida undergoes a change which prevents additional sperm from entering the egg. The embryologist can detect evidence of fertilization the next day. This is considered day 1.
ICSI – Intracytoplasmic Sperm Injection
ICSI is used in place of conventional insemination when sperm counts are abnormal, or there is a risk that eggs may not fertilize with conventional insemination. During the ICSI procedure, the outer cells around an egg are stripped away using very fine needles. This exposes the egg to the embryologist who can make an assessment as to the quality of the egg. The embryologist can now position the egg for the sperm injection step of the process. Sperm used for ICSI undergo a sorting process that helps to isolate motile sperm that appear visibly normal. An individual sperm is loaded into a tiny needle and injected into the egg. This delivers the DNA content of the sperm directly into the egg. An embryologist’s experience with ICSI can have a significant impact on the success of ICSI treatments. Our staff have decades of experience with ICSI procedures and have made modifications to the process that have enhanced fertilization and even the rate of blastocyst development and embryo grading. California IVF is conducting investigations into the conditions surrounding ICSI and fertilization as a means to improve pregnancy outcomes.
Fertilization Check
The day after the sperm and eggs have been put together by ICSI or conventional insemination, the eggs should show signs of fertilization. A normally fertilized egg is called a 2PN for 2 pro-nuclei. These two structures represent the male and female DNA. These DNA packages will unite and give the resulting embryo its unique DNA. Not all eggs will fertilize normally. The embryologist will also take note of the egg quality on this day, known as “day 1”. Patients receive a fertilization report that informs them of the outcomes of the fertilization process.
Abnormal Fertilization
Several abnormalities can happen during the fertilization process. These are generally things we do not want to see since the egg is no longer capable of producing a normal embryo
3 PN – a 3PN embryo has 3 complete sets of DNA. This can happen if the egg does not get rid of the extra set of DNA produced by the cell division process called meiosis. This can also occur if more than one sperm enters an egg during conventional insemination.
GV – Germinal vesicle. This is an egg that was too immature to fertilize. Often small follicles on ultrasound (fluid sacs containing eggs) will produce immature eggs. Women with decreasing egg quality will often have a higher than normal portion of eggs that are GV’s. It is also quite normal to find a few GV’s with IVF treatment.
Dark/Atretic Oocyte – an egg that has compromised quality or is no longer thriving will often take on a dark and grainy appearance. Finding an atretic egg is a hallmark sign that the egg is dying, or has died, and will no longer progress. Endometriosis, increasing age, and chromosome abnormalities within the egg can cause the appearance of these types of eggs. It is less common to see these problems in eggs from a young healthy woman such as an egg donor.
Non-fert – A non-fertilized egg generally indicates the failure of the egg or sperm to properly combine their DNA. On a few occasions, fertilization may have taken place normally, but the 2PN stage is not seen by the embryologist. Non-fertilized eggs are often observed for a period of time to evaluate them for progression to embryos.
1 PN – a 1PN embryo is similar to a non-fertilized egg in the sense that there are chances the egg may progress to an embryo. The occurrence of a 1 PN embryo means one gamete produced a pro-nuclear structure but the DNA from one gamete (the sperm, for example) is missing. It is normal to see 1 PN embryos during the course of IVF as long as the overall proportion of 1 PN embryos remains small.
Vacuoles – vacuoles are cystic fluid collections within the egg that usually represent abnormal cell chemistry. This is a hallmark sign of compromised oocyte quality. Embryos have been known to progress well and make a pregnancy despite the initial appearance of a problem. If a high percentage of eggs show vacuoles, the pregnancy rate is usually reduced. There is not an effective treatment to prevent or correct this from happening, though our staff and researchers continue to work on ways to improve the rates of success in the setting of poor egg quality.
Egg Class
Egg class is the name given to our educational seminar conducted by one of our senior embryologists. During this class, patients learn about the various procedures performed during the embryology portion of the IVF treatment. This class has been widely praised. Various industry vendors for equipment and pharmaceuticals send their new employees to our Egg Class because of the enthusiasm and articulate presentation of the material. California IVF is thankful to have superb embryologists that are admired and appreciated by patients and staff alike. Participants in the California IVF Egg Class know their embryos are in good hands. If you are planning IVF treatment, you want to work with a team you can feel confident will provide the best possible care. Our family is here to help with your goals of becoming a parent.