Stephen J. Schueler, M.D.

Pregnancy Step 2 Fertilization

Our genetic material is carried in structures known as chromosomes. Our chromosomes provide the specific "blueprint" for producing a human being. The egg and the sperm each contribute one-half of the genetic material, or chromosomes, required to produce a human being.

During fertilization, millions of sperm will try to enter the egg in an attempt to share its genetic material. If one sperm is successful, the resulting organism will have a complete set of 46 chromosomes. Without fertilization, the egg does not have enough genetic material to produce a human being and will eventually die.

Conception is the moment when a single sperm successfully passes inside the egg and completes the necessary number of chromosomes necessary for life. At this point, no other sperm can enter the egg. Fertilization and conception usually occurs when the egg is making the trip through the fallopian tube from the ovary to the uterus.

Conception triggers a rapid process of repeated cell divisions and growth. One cell becomes two, two become four, and so on. Several days later it will arrive at the uterus. At this time it is only a collection of cells, known as a blastocyst. A blastocyst is so small that a microscope is needed to see it.

Continue to Pregnancy Step 3 Implantation

Last Updated: Jul 7, 2009 References
Authors: Stephen J. Schueler, MD; John H. Beckett, MD; D. Scott Gettings, MD
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