What is Egg, Sperm and Embryo?

Egg, Sperm and Embryo

You have gone to a restaurant, ordered a salad which doesn’t taste as great as it should.  On closer look you realise that the vegetables are not fresh. Just as the success of a dish depends on the ingredients that go into it, the number and quality of embryos or the success of the cycle largely depends on the egg and sperm; both being equal partners. Poor quality of either can affect the outcome. The sperms, egg, and embryo – all need a controlled-environment and only trained people should handle them. While visiting a clinic, it should be borne in mind that embryologists are qualified to handle eggs, sperms and embryos, whereas an andrologist is limited to the handling of the male counterpart of eggs or sperms. If the clinic has only an andrologist on its staff, this should raise a red flag, and it is advisable for patients to ask questions on the staff capacity of the clinic.


Unlike other medical procedures, assisted reproduction offers you a second, third, fourth… umpteen number of chances. Most times couples believe that if their first attempt does not work, the second attempt will not work either or they feel that if they try a second time the chances of conceiving increase because success is cumulative. Well, it’s sometimes difficult to counsel them that consecutive attempts hold neither lesser nor greater chances of conception. Yes, your doctor will try to modify your treatment protocol to achieve better success rates in the next cycle by supporting your treatment with well-proven scientific techniques like Magnetic-Activated Cell Sorting (MACS) and Preimplantation Genetic Screening (PGS) or sometimes with adjuvant therapies like endometrial scratching, intralipid infusion, and so on. Whatever your doctor advises it’s for your benefit and for a better outcome. As consultants, doctors and scientists, success matters to the IVF team as much as it does to the patient.

The three key players or the stars at fertility clinics are:

  1. Egg/Oocyte/Ovum
  2. Sperm
  3. Embryo

The Egg

The egg is one of the largest cells in the human body; in fact, it is a giant compared to other cells in the body. No other cell in the body is anywhere quite as big. Yet it is not large enough to be seen by the naked eye. It should be remembered that everything examined inside the embryology lab is microscopic. Women are born with approximately two million eggs which keep diminishing as the age progresses. Naturally, the first day of menstruation, when the bleeding starts, is counted as the first day of the cycle. One of the ovaries will release an egg (ovulation) about 14 days before the start of periods. Eggs are released randomly by any one of the two ovaries.

An egg lives in the fallopian tubes for about 12-24 hours after ovulation. Of the three players, the oocyte or the egg is the most important component. The success of the treatment depends on the quality of the oocyte. The oocyte ages as the maternal age goes up. Oocyte quality matters more than quantity. Remember it just takes one good oocyte to achieve a pregnancy. Your clinician can evaluate the number of eggs present in the ovary through hormonal testing and ultrasound scanning.

Nature’s bonus!

Multiple ovulation is the release of two or more mature eggs during a cycle. This is said to occur in up to 10% of all cycles, which means that the average woman releases two (or more) eggs at least once a year! When two eggs are released and both are fertilized, this produces fraternal twins.

The Sperm

The sperm, the male reproductive cell or gamete is produced in the testis. Male-ejaculate known as semen is a combination of various hormones; fluids which provide sperm with the energy to be motile. A person ejaculating may not necessarily have sperms, as the semen may or may not contain sperms. A healthy adult male can release millions of sperm cells in a single ejaculation. However, for the IVF procedure just a few sperms are needed. Remember, it just takes one egg and one sperm to achieve a pregnancy. The typical lifespan of sperm in a woman’s body while fertile cervical fluid is present is three days, but in the right conditions sperm can even live up to five days. Whilst maternal age does have an effect on the egg, paternal age does not have a major impact on the count, motility, and morphology of the sperm.

Is it a girl? Is it a boy?

In our male dominated society, often the woman goes through the pressure of producing a male offspring. The fact, however, is that the egg (and hence, the woman) has no role in affecting the gender of the resulting embryo. The sex-determining chromosome is carried by the sperm, which means, you could think of the sperm as being either “male” or “female”. So, the sperm is either a “boy” or “girl” from the moment it is formed in the testes. Which of these sperms fertilizes the egg will determine the sex of the baby. This is nature’s rule.


Sperm and Male Infertility 

Although fertility problems have often been considered a female problem, this isn’t always the case. Approximately half of all couples coming to the fertility clinic for evaluation find they have a problem with the sperm. Although this can often leave the male partner feeling guilty and confused, it’s important to remember that infertility is a problem of the couple and is a shared challenge, no matter where the diagnosis lies.

The Male Reproductive System

The testes are the most important part of the male reproductive system. This is where sperms are made and stored, as well as the site of testosterone production, the hormone that gives men their masculine characteristics and helps sperm development.

The Role of Sperm in Fertilization

After ejaculation, the sperms swim through the cervical mucus and enter the uterus. They then swim up into the fallopian tubes where they meet an egg at the far end closest to the ovary. Although millions of sperms are deposited in the vagina, only a couple of hundred reach the egg.

Causes of Male Infertility

Sometimes the male partner is found to have a problem with his sperm. A semen analysis at your local fertility clinic will identify problems involving the sperm count (numbers) and morphology (the shape and size) or motility (the movement). If a specific problem is identified, then the cause can be investigated by a specialist. Most often, the only advice is to change environmental and lifestyle factors that may be contributing to a low sperm count. But occasionally, further testing is needed to eliminate underlying health conditions or undiagnosed genetic disorders.

Sperm Quality Factors in Male Infertility

Sperm quality influences not only rates of fertilization but also the subsequent embryo development. Remember, half of the genes come from the father. The male partner may carry a chromosomal abnormality that is responsible for him having a low sperm count and that increases the risk of implantation failure and miscarriage.

Semen Analysis

A standard semen analysis usually tests sperm count, motility, and morphology. Several tests that are more advanced can be carried out if the sperm count is low for no apparent reason or if several treatment cycles fail without explanation.

One of the first investigations done by a fertility doctor is a semen analysis. This is done after the man has masturbates and collected his semen into a sterile container. You can produce the sample at the clinic in a special room or at home if you live close by. The clinic will supply you with a container

When you get your semen assessment done, your doctor will receive a report from the lab with all the findings. The following table shows the normal ranges for sperm count, motility and morphology.

The most important factors are the sperm count and motility, and this will determine the suggested treatment options for the couple.

After Semen Analysis

Problems with the sperm not diagnosed by standard parameters of a semen analysis are:

These conditions can be ruled out with advanced tests like DNA Fragmentation Index (DFI), MACS, PGS discussed in chapter 10. Often, semen analysis results from a pathology lab differ from the results at a fertility clinic. Semen analysis at a fertility clinic is the most accurate predictor in such cases.



An embryo is the result of a mature egg that has been fertilized by a sperm in the woman’s reproductive system, or in a lab-based environment during assisted reproductive treatments. During in-vitro fertilization (IVF), sperms and eggs are collected from couples undergoing the treatment, and the embryo is generated in the lab. Embryos are grown in the lab in incubators using small dishes knows as petri dishes, not in the test tube as the myth goes, under strictly controlled conditions. They are then transferred to the woman’s uterus for implantation and growth at an appropriate stage of embryo development. The decision to do a transfer at the cleavage stage or blastocyst stage is a well-thought-out decision jointly taken by the couple, their clinician, and the embryologist.

These stages are explained along with the advantage of blastocyst-stage transfer using the following example.Mr. & Mrs. Vyas, a couple going on IVF treatment at a clinic asked the embryologist about the stages. The embryologist said, “Sure, I can explain. Depending on the day of development, embryos are either in their cleavage or blastocyst stage. Cleavage-stage embryos are in their second or third day of development. On the other hand, blastocyst-stage embryos are in their fifth or sixth day of development. The blastocyst-stage embryo has an inner group of cells that transform into the fetus and a second, outer group of cells that will turn into the placenta. This is the last stage until which an embryo can be grown in the lab. The blastocyst stage is the preferred stage of embryo transfer. At this stage, the embryo implants onto the uterine wall and continues to grow while being protected by and receiving nourishment from the rich uterine lining.” Mrs. Vyas responded, “Thanks for making it simple. Now it doesn’t sound at all that strange.” On the day of transfer, the embryologist approached the couple to explain the embryo report before the embryo transfer. She said, “After weighing the pros and cons we have decided to transfer 2 blastocysts for you.” Mrs. Vyas asked, “Can we please know the weight and sex of the embryo being transferred?” The embryologist explained, “An embryo is microscopic. It is impossible to determine its weight and sex.”

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