How is the egg fertilised and how long does it take to nest?

Fertilization of the egg by sperm and its subsequent nesting in the uterus are the beginning of pregnancy.

You often ask:
How does the egg get fertilized and how does it manifest itself?
How long does it take for the sperm to reach the egg?
What are the developmental stages of a fertilized egg?
How long does it take for the egg to nest in the uterus?

At the moment a woman learns from her gynaecologist that she is pregnant, the birth of a new life is still tiny. By ultrasound, we can see it as a dot. It is almost unreal that from this dot, the union of two sex cells begins to develop a new life that will see the light of day only a few months later.

How did the egg get fertilised, what developmental stages did it go through and how did it nestle in the womb?

There are approximately 400,000 immature eggs in a woman's ovaries until her first menstrual period. From the first menstrual period onwards, one of these eggs matures every month and can be fertilised. A woman has the possibility of becoming pregnant up to 400 times during her fertile years (if we take this mathematically).

How does fertilization occur?

Fertilisation occurs during sexual intercourse.

It is the fusion of a male and a female sex cell. When two cells, a female (egg) and a male (sperm), unnoticeably and invisibly fuse together, a new life can be created. A new human being, unique, develops from the mixed hereditary genes of the mother and father. This phenomenon, even if thoroughly studied, will always remain unique.

Fertilization of the egg, symptoms, is fertilization felt?

When planning a family, expectant mothers from the beginning carefully observe all the signs of pregnancy. They often ask whether it is possible to feel fertilization.

Fertilization of the egg is not felt, although it happens inside the woman's womb in the tube of the fallopian tube and uterus.

The first, earliest very faintly observable symptom may be a very slight pain in the lower abdomen. This has been noted by some women (in rare cases) when the egg has nestled in the uterus.

It is only as it gradually attaches with the blood vessels that changes begin to happen in the female body and the hCG hormone begins to be produced. This is a chorionic gonadotropic hormone. It is produced initially in very small amounts which increase day by day.

HCG can be detected around day 7-10 after fertilization using a very sensitive pregnancy test.

When is the right time for fertilization?

The menstrual cycle has its phases. During these phases, the uterus is cleansed, the egg matures, the uterine lining grows again, the blood supply increases and the woman's body prepares to receive the fertilised egg so that a new life can be created.

If this does not happen, the monthly cycle of cleaning and preparation for fertilization follows again.

It is a good idea for every woman to know her menstrual cycle and to keep a record of it, so that she can better calculate her fertile days and any disturbances in her cycle. Counting fertile days, taking basal temperature or even ovulation tests can be used to find out when ovulation has occurred.

Interesting information in the articles:

• How to plan pregnancy?
• How does the ovulation test work, when to test, what confirms positivity?
• The first signs of pregnancy. How to recognize them?

Each egg is surrounded by a shell - a follicle.

At the beginning of a woman's menstrual cycle, hormones begin to be produced, which motivate the growth of the number of cells of the follicle (the envelope gets bigger). This also makes the egg bigger, around which a fluid is also formed - the Graaf follicle.

Around day 14 of the cycle, another hormone plays a role. By increasing the amount of this hormone, the follicle begins to grow rapidly and the egg matures. By this time, the enlargement is so great that it forms a bulge on the ovary.

The Graafian follicle bursts after the egg has matured and the egg is released into the abdominal cavity. This is called ovulation.

In the meantime, the egg has become encased in a fine membrane and a ring of follicular cells that have substances in them that repel late sperm. After ovulation, Graaff's follicle turns into a yellow corpuscle.

The egg, released into the abdominal cavity, is drawn through the funnel hole into the fallopian tube.

During ovulation, some women feel a tugging or slight pain in the lower abdomen.

Read also the article.

The fallopian tube is lined with fine cilia that transport the egg through the fallopian tube into the uterus. This is when the fight against time begins.

Within a maximum of 12-24 hours, the egg is ready to unite with one of the millions of sperm during ejaculation, which reach the fallopian tube with great speed and mobility. If the mucus in the vagina is thin, the sperm move better in it, and so their movement is faster and smoother.

Barely a thousand sperm out of a million manage to penetrate the fallopian tube. They move around the ovum and try to enter its interior.

If the sperm penetrate the fallopian tube and the egg is not inside, they stay on the wall of the fallopian tube and wait. The life span of sperm is 48 hours, but some survive for 3 days. If ovulation occurs during this time, the sperm catch the egg and start towards it.

As the sperm conquers the egg, it releases an enzyme that dissolves the egg's envelope so that it can enter. Only one, the most vital, the fastest, will make it.

Once inside the egg, the sperm loses its flagellum and the egg immediately sends a signal. Its protective membrane turns into an impregnable barrier.

Inside the egg at that time is the cell nucleus of the sperm and the nucleus of the egg.

In a short time, the two cells come together and a great moment ensues. The two cells fuse and new life is born.

Day 1

Fertilization is the fusion of the female germ cell (egg) with the male germ cell (sperm).

The two have half the number of chromosomes, 23 (23 chromosomes from the mother and 23 chromosomes from the father). When they fuse, they form a single cell that contains different genes, hereditary information from both parents. This creates a new unique being with a chromosome number of 46 XX (predetermines female sex) or XY (male sex).

This fusion of cells is called a zygote. It takes 24 hours.

After fertilisation, the egg moves from the fallopian tube towards the uterus by means of cilia.

The inside of the fallopian tube is quite bumpy, which, even with the help of the cilia, makes it easier for the fertilized egg to travel towards the uterus. But in rare cases, it may happen that the egg gets stuck on an obstacle. In this case, an ectopic pregnancy may occur (gravidita extrauterina).

How does an ectopic pregnancy manifest itself? Know the symptoms early

Approximately 20-30 hours after the union, the cell begins to divide.

Day 2

The first cell division of the zygote produces a blastomere, a mitotic cell division (a separate division of the cell and cell nucleus in which the number of chromosomes in the daughter nuclei is preserved). One cell divides into two equal parts with the same number of chromosomes of the zygote through a complex process.

During this time, the fertilized egg travels to the uterus (the egg migrates).

Each subsequent cell division occurs approximately every 20 hours.

Day 3

After fertilization, the egg is composed of 8 cells. These resemble the mulberry tree in appearance and are called morula.

At the end of the day, it is already made up of 16 cells. Probably at that time, it has already entered the uterus, the lining of which has changed in the meantime. This impulse to prepare the uterus is sent by the follicle, which first releases the egg.

The uterus is swollen, well blooded and ready for the egg to nest.

Day 4

Cell division continues. The cells forming the envelope (trophoblast) are differentiated. This forms the placenta, which will nourish the fetus throughout its development until birth. The outer sheet of the amniotic membranes (chorion) is also formed.

Inside, a cluster of larger cells (the germarium) adheres to the integument, from which the fetus develops.

In the morula, a hollow nucleus with fluid in the form of a sac has formed. This stage is called the blastula. It then changes into the blastocyst, an already divided egg that has an outer and inner mass divided by fluid. All its cells are identical and only later form into different units.

At this time, it is already in the uterus.

Day 5

The cells of the superficial trophoblast release an enzyme that dissolves the epithelial cells (surface lining) of the uterus. Nesting begins.

Meanwhile, the egg continues to develop and improve.

Day 6

The blastocyst burrows into the uterine lining and nidates.

The trophoblast, which will nourish the embryo throughout, begins to divide. It slowly grows into the uterine lining.

Day 7

One week after fertilization, the blastocyst with 150 cells nests in the uterus.

The blastocyst burrows deeper, implants itself, dissolves the endothelium of the uterine blood vessels and comes into contact with the maternal blood.

On this day, the egg is finished nesting in the uterus.

The trophoblast is now fully adhered to the uterine wall and begins to produce hCG (human chorionic gonadotropin).

The hCG lets us know that after a difficult and arduous journey, the egg has nested in the uterus and is connected to the mother by blood. It lets us know that it is okay.

It takes about 13 days for the egg to become firmly established in the uterus.

Some women notice very light bleeding lasting 1-2 days on the 11th-12th day after fertilization, which some women may mistake for menstruation.

How do monozygotic or dizygotic twins form?

Monozygotic twins are formed by fertilization of one egg and one sperm. One fertilized egg divides into two identical parts between the cell division stage and the first stage of fetal development.

Identical twins are always the same sex and have the same genetic basis. But even identical twins with the same (identical) set of chromosomes are not the same. Each has different temperaments, abilities and talents. Even identical twins have different fingerprints.

The odds of identical twins being born are 1 in 250.

Identical twins are created by fertilizing one egg with two sperm cells that have penetrated the egg. Or, two eggs are released in a woman's body and fertilized at the same time. If one sperm cell carries a female cell, a girl is born, and if the other carries a male cell, a boy is born.

These twins are different in most cases. They have different sexes, different eye colour, hair colour, appearance. But it's not a rule. They can look very similar to each other, as if they were identical.

Triplets are usually multiples, very rarely are triplets born singletons.

Quadruplets, quintuplets, and even multiples are a common result of hormone treatment for infertility at this time.

Interesting facts about sex cells.

Sperm:

• A healthy adult male produces up to 50 million sperm per day
• the quantity of ejaculate under normal circumstances is 2-6 millilitres
• 1 millilitre has 20 to 120 million sperm in it
• sperm measure only 0.06 mm
• it takes approximately 2-3 months for sperm to mature
• the lifetime of sperm after ejaculation is 30 seconds (inside the female body, in the uterus, they can survive up to 6 days)
• in order for a woman to be impregnated, the sperm must be introduced directly into the vagina

The sperm dies very quickly until it enters the vagina.

Egg:

• the size of the egg is approximately 0.1 mm
• the lifetime of the egg is 12-24 hours
• one egg is released each month during the menstrual cycle
• by the time the foetus develops in the third week, the woman's ovaries have already begun to form and at that time contain approximately 100 germ cells
• During a woman's fertile lifetime, around 400 eggs may be released