Fertilization – When Exactly Does Conception Begin?

Even before you get a positive result of your pregnancy test, the fertilized egg would already have started the process of development. Conception has therefore begun.

Conception begins as soon as an egg cell is fertilized by a sperm cell.

Within the first five days of fertilization, the egg would have moved down the fallopian tubes and into the uterus. While moving down the fallopian tube to find its way into the uterus, the egg starts to produce hormones which will help prepare the lining of the uterus to receive the new baby.


The process by which the normal lining of a non-pregnant woman is changed to the much thicker lining of pregnancy is very important for once the egg has reached the uterus it must implant itself into the lining.

For implantation to occur, more enzymes are called into play. These enable the developing egg to penetrate fully into the lining and then start the process by which a placenta is formed.

The placenta is the important organ which nourishes the baby during the whole of its life in the uterus. Implantation of the fertilized egg is completed by about eight days after fertilization has occurred.

Over the succeeding twelve weeks the egg will continue to grow to fill the cavity of the uterus. As the baby grows, the uterus will continue to enlarge influenced by the hormones produced by the developing egg and by the mother's ovaries.

By the twelfth week, the uterus will have been completely filled with the developing baby, which has become a fetus with umbilical cord and placenta.

During these first twelve weeks while the transformation of the fertilized egg is proceeding, the embryo is sensitive to outside influences.

If you are pregnant at the moment, Is your pregnancy a planned pregnancy or unplanned pregnancy?

Factor that could affect the developing baby

There are several factors that may have adverse effects on the developing baby:

1. Viral infections

The following types of viruses could affect the baby when the mother catches these disease when pregnant.

Rubella virus, cytomegalovirus, herpes virus and toxoplasma.

Virus infections like the flu may affect the baby although its effect may be less severe than that of German measles.

2. Drugs like thalidomide have very serious effects on the baby.

Thalidomide is a kind of drug that was intended for the treatment of sleep disorders and morning sickness.

3. Smoking

4. The mother's emotional state

Types of Fertilization

In Vitro Fertilization (IVF)

In vitro fertilization is an out-of-the-body union of an egg or sperm. IVF is used as alternative to getting pregnant if the natural method is not successful.

The phrase "in vitro" which means glass, is used to describe this method of fertilization because early scientists used glass, for example petri dishes, test tubes and beakers, to carry out their experiments.

© 2012 WAHmom

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Comments 7 comments

WAHmom profile image

WAHmom 2 years ago Author

crissy30, you need to consult your OB-GYN for proper medical guidance on getting pregnant. Good luck and be well.


chrissy30 profile image

chrissy30 4 years ago

My husband and I are trying to conceive. I had been on the depo shot for 7 years after the birth of our first child and then stopped using this. I started having regular periods again. Then in May of 2011 I went back on it, but didn't go back for a second shot. I then again started having periods regularly. My last period was on Dec. 27th and they usually last for 5 days. This one went like this I bled on the 27th and 28th, stopped on the 29th, and then started bleeding again on the 30th and 31st. I had sex on Jan. 1st, 4th, and 6th taking that my ovulation day should have been around the 8th, I am having all the symptoms but I am scared of taking a home test due to getting a negative result. What should I do?


WAHmom profile image

WAHmom 4 years ago Author

Hello Thesingernurse,

Your comment is very enriching to the readers because it gave them additional information about this stage of pregnancy. Thanks a lot!


thesingernurse profile image

thesingernurse 4 years ago from Rizal, Philippines

Very concise and informative description. You are right. The first 12 weeks or the first trimester is the most crucial trimester of pregnancy. Here's the time when the embryo is on its way to become a fully matured fetus. Although it is the rule of the thumb to protect the mother from external factors all throughout the pregnancy, this period is especially sensitive because this is the time when the embryo undergoes ORGANOGENESIS. Organogenesis is the process of development of various cellular, tissue, and organ structures of the fetus which will later on mature and fully develop at term.


WayneDave profile image

WayneDave 4 years ago from Leeds, England

No probelem!!


WAHmom profile image

WAHmom 4 years ago Author

Thanks for dropping by, Wayne.


WayneDave profile image

WayneDave 4 years ago from Leeds, England

Very informative. Thanks for sharing.

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