Egg Retrieval and Evaluation in IVF
IVF requires a safe, effective, and efficient method to obtain a woman’s eggs. During the early years of my training, it was hard to believe that we had to perform a laparoscopy to retrieve eggs. Laparoscopy is a surgery done under general anesthesia in which a periscope called a laparoscope is inserted into the body. We insufflated the abdomen and pelvis with carbon dioxide gas. All pelvic organs were easily identified and manipulated with long, thin probes.
Under direct vision, we punctured each follicle and sucked out all of its fluid. Our goal was to find the microscopic egg in this collection of fluid. Technological advancements have allowed us to retrieve eggs through the vagina using a simple office procedure. A complicated process has now been transformed into a 30-minute procedure through the vagina.
No general anesthesia is required. The patient is not subjected to any invasive procedure which requires entering the abdomen with surgical instruments.
What is the Concept of Vaginal Egg Retrieval?
When retrieval through the vagina was first introduced, it was assumed that it would limit the number of follicles to be drained and the number of eggs to be retrieved. The exact opposite is true. At laparoscopy, the reproductive endocrinologist and surgeon can only pierce and drain the follicles that are visible to the naked eye. Using an ultrasound probe, we can identify all the follicles in the ovary, not just the ones on the surface. We can traverse the ovary with the ultrasound probe, identify and aspirate any follicle present anywhere, and retrieve each egg, called an ovum. The ultrasound waves create images based on the contrast between fluid and solid. The fact that the follicles are completely fluid-filled and surrounded by thick tissue from the ovary allows easy identification of each follicle. The ultrasound probe is an elongated device with a smooth, round surface at the end.
How Are Eggs Retrieved Through the Vagina?
The process of retrieving the eggs is simple. Each egg is within a single follicle. A needle is placed safely alongside the length of the ultrasound probe. Suction is applied to the back end of the needle. In this way, I can aspirate each follicle. The fluid from the follicle is collected into a test tube. It is remarkable that once the needle is inserted into the ovary, it can be manipulated to reach all of the follicles, one at a time. Usually, it is only necessary to reposition the needle in the ovary one or two times.
Each test tube, consisting of follicular fluid and an egg, is passed to the laboratory personnel. The embryologist pours the fluid into a flat, circular petri dish. The eggs are then identified using a low-powered microscope. Mild sedation ensures you feel no pain or discomfort during egg retrieval. To simplify things, I often use so-called ‘conscious sedation.’ This consists of a muscle relaxant in conjunction with small doses of pain medication. You may feel some minor cramping for a day or so. Following the egg retrieval, you will rest for 30–60 minutes.
What Is the Ideal Number of Eggs to Retrieve?
The sweet spot for the number of eggs I hope to retrieve is between 10 and 19. I like to tell my patients that a ‘baker’s dozen’ would be fine. Of course, a baker’s dozen is 13 eggs. If we have an inordinate number of eggs, the likelihood of immaturity and disruption of the eggs increases. If we have too few mature eggs, then we will have a reduced number of normal embryos. Generally, 8 to 18 eggs are retrieved from a woman’s ovaries with IVF. However, it is not the number of eggs that matters but the quality.
If we talk about success rates, one high-quality egg is better than 20 poor-quality eggs. Not all of them are viable for fertilization. On average, 80% will have the appropriate maturity and integrity needed for IVF. Follicles larger than 14–18mm most likely have genetically mature eggs. The fluid within each follicle can range from about 1 ml to 10 ml. Within this pool of fluid resides a microscopic egg measuring 120 millionths of a meter.
How Does the Laboratory Assess Eggs?
The staff of the IVF laboratory consists of a Ph.D. laboratory director certified in assisted reproductive procedures. Two or three highly trained medical technologists also assist in the laboratory. In most cases, the fluid aspirated from the follicle will contain an egg, but not always. The first goal of the lab is to determine how many eggs look mature and intact. A collection of tiny cells spread out around the egg in a fan-like configuration. These are called cumulus cells. They are supportive elements for the egg. The cumulus cells are teased away with needle-like instruments to get a good look at the egg. An egg with an excellent appearance will have a round shape, a uniform appearance, and a circular coating around the cell called the zona pellucida.
Each egg is graded according to a standardized system. This is based on whether the eggs appear mature or immature. The eggs can be atretic, meaning they are without form or are breaking down.
What are M2 Eggs?
Eggs go through two genetic stages, meiosis I and meiosis II. The letter M stand stands for a genetic phase called ‘metaphase.’ The ‘2’ stands for the second meiosis. M2 eggs are the mature eggs. The goal of hormone stimulation of the ovaries is to produce as many M2 cells as possible. These are the ones that are most likely to undergo successful fertilization. This is because they are genetically mature. Mature eggs remain in the M2 stage until fertilization occurs. M1 cells, from the metaphase of the first meiotic division, are immature. Sometimes, they will mature one day later in the lab.
A small, round structure called a polar body is an important feature of a mature egg. It is located outside the egg’s surface membrane just inside the zona pellucida. Polar bodies have a duplicate set of the egg’s chromosomes, which are mirror images of the chromosomes within the egg. They can be teased out and genetically tested in the lab. This is called polar body diagnosis. This is rarely done because we prefer to test Day 5 embryos (blastocysts).
What Should You Know After Egg Retrieval?
After the egg retrieval, all my couples are informed of the following:
- The number of mature M2 eggs.
- The number of immature cells.
- The number of disintegrating cells (atretic).
Germinal vesicles signify the most immature egg cell. They have an immature nuclear membrane. The germinal vesicle egg, retrieved during an IVF cycle, will not undergo successful fertilization.
Why Aren’t All Eggs Normal With IVF?
About 15–25% of eggs are likely to be immature following egg retrieval—a surprisingly high number. Furthermore, even mature eggs can have an abnormal number of chromosomes. This is called aneuploidy. About 10–30% of the eggs of women in their 30s will be genetically abnormal. For a woman in her 40s, more than 50–80% of the eggs will be genetically abnormal. The hormone regimen used to stimulate the ovaries affects the number and quality of eggs. If an IVF cycle fails because of poor egg quality and reduced numbers, the regimen is altered.
Normal-appearing eggs will sometimes fail to fertilize despite the use of healthy sperm. Sometimes, the egg undergoes fertilization successfully, but an embryo will not form or grow. Multiple research studies have shown that in over 90% of cases, these defects are due to the egg, not the sperm. Having normal chromosomes is the main defining attribute of a normal egg.
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