Conception: Miracle of Life (From Ovulation and Fertilization)

Conception of the Egg and Sperm to a Fetus

From Fertilization to Fetal Development – The Miracle of Life

The process from pre-conception to conception is a complicated one. After conception, the fertilized embryo develops into a fetus. Let us look at each stage of the fetal development in more detail.

After ejaculation of the sperm into the vagina, it travels into the uterus. Out of 200 million sperm, only approximately 500-600 would reach the fallopian tubes.

About 7-8 days after fertilization, the trophoblast develops finger-like projections to help the blastocyst burrow into the nutrient-rich endometrium for implantation.

The sperm and egg will meet which we call conception. Both will combine to form a fertilized egg. The fertilized egg takes approximately 3-4 days to reach the uterus. Between 5-7 days after fertilization, the fertilized egg will implant on the endometrium and begin fetal development.

A Mother’s Seed of Life - Egg

The egg is different from the sperm in many ways. In terms of size, it is approximately 0.1mm and 10 times larger than the sperm. The large size of the egg is due to its nucleus and the nutrients cytoplasm of the cell. Part of the cytoplasm of the fertilized egg will transform into energy required for cell division, while the remaining portion consist of matter that will eventually develop into the fetus. Each follicle resembles a tiny blister and consists of an egg. Every month from puberty till menopause, a follicle will ovulate and produce an egg during the ovulation period.

Normally only one egg is released each time during ovulation, so the rest of the follicles that attempted to ovulate at the same time will degrade before complete maturation. As an egg only lives 12-24 hours after leaving the ovary, it will have to be in contact with a sperm within this duration to be fertilized.

The process of ovulation rotates between the two ovaries and there are only around 300-500 ovulations in a woman’s lifetime. Ovulation occurs on the 14th day in a 28 days menstrual cycle. After ovulation, the follicle proceeds to form and secrete progesterone to nourish the endometrium, in preparation of the egg’s implantation if a successful fertilization takes place.

A Father’s Seed of Life - Sperm

The sperm is manufactured in the seminiferous tubules within the testes and halfway through maturation, they are transported to the epididymis until they are fully matured. At ejaculation, the sperm are propelled through the vas deferens located within the spermatic cord and into the abdominal cavity before joining at the seminal vesicles, which add alkaline fluid to form semen. A sperm consists of 3 components which are the head, body and tail. Shaped like a tadpole, a sperm is 0.05mm in length and cannot be seen with the naked eye. The head of a sperm is a nucleus containing the chromosomes, completely covered by a sticky layer of acrosome. During fertilization, the acrosome corrodes the wall of the egg to allow the penetration of the sperm’s head into the egg.

The sperm’s body contains small energy factories called mitochondria, which provides it with energy to propel towards the egg. Finally, the sperm’s tail helps it to swim through liquids.

Each ejaculation contains approximately 200 million sperm, but only one sperm will be used to fertilize the egg. Among these 200 million sperm, 40% of them are abnormal and will not be suitable for fertilization. These sperms will be eliminated or will die before reaching the egg. The vaginal environment is acidic, whereas semen is alkaline so a sperm have to endure the harshest environment in order to qualify for fertilization. This elimination process will ensure that only the strongest sperm among the 200 million sperm count is able to make it into the uterus.

After entering the uterus, the next hurdle for the sperm is to swim upstream through the fallopian tubes towards the ovary. This journey takes around 2 hours. Along the way, small amounts of mucus will be secreted from the fallopian tube, so the sperm needs to swim upstream against the relentless flow. Among the 200 million sperm, only around 500-600 sperm reach the fallopian tubes. The remaining sperm that reached the fallopian tubes but were not used to fertilize the egg will then be degraded at a discharge zone.

The Beginning of Life - Conception

Eggs from the ovaries do not possess the same mobility as sperms, so it will be transported towards the uterus via mucus from the fallopian tubes, until it comes in contact with a healthy sperm and be fertilized. The acrosome layer on the head of the sperm is made up of enzymes capable of dissolving the egg’s wall. Once the wall is partially dissolved, the head of the sperm will penetrate into the egg swiftly, leaving behind its tail.

Have you ever wondered if two or more sperms will enter the egg concurrently? Rest assured that this situation would not be allowed to occur. The moment a sperm successfully penetrated into the egg, the egg exudes an instantaneous reaction to prevent any more sperm from making their way in. The egg contains 23 chromosomes and the sperm contains another 23 chromosomes. Once all 46 chromosomes are in set place, the process of cell division will begin.

Successful Pregnancy - Implantation

Within the first 30 hours after fertilization, the chromosomes from both the sperm and eggs will fuse and form a new cell known as the embryo. Around 3-4 days after fertilization, the fertilized egg will move further along the fallopian tubes and towards the uterus, while the embryo is being formed. Implantation of the fertilized egg into the endometrium occurs around 5-7 days after fertilization.

The entire process starting from the Cilia tubal wall transporting the fertilized egg towards the uterus, hormonal changes from the uterine wall, thickening of blood vessels, are all crucial parts of an elaborate implantation process. When the embryo is successfully implanted in the endometrium, it is already the third week of pregnancy. During these three weeks, if any of the implantation process was not performed successfully, pregnancy would not be able to occur and will deem to have failed. The process from a live embryo in the endometrium to the development of facial features and organs takes 12 weeks. After 12 weeks of development, the embryo is now known as the fetus.

Best said that conception is the start of a beautiful life for a human being.

Sandra Henderson
 

Editor-in-chief at Babiology and a proud mother of four passionate about sharing pregnancy and baby growth knowledges

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