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How Pregnancy (Conception) Occurs - Topic Overview

Most women are able to become pregnant from puberty, when their menstrual cycles begin, until menopause, when their cycles stop. A pregnancy starts with fertilization, when a woman's egg joins with a man's sperm. Fertilization usually takes place in a fallopian tube camera.gif that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing.

Ovulation, fertilization, implantation

All the eggs for a woman's lifetime are stored in her ovaries. Women do not keep producing eggs. This is different from men, who continuously make more sperm.

About once a month, an egg is released camera.gif from one of a woman's two ovaries. This is called ovulation. The egg then enters the nearby fallopian tube that leads to the uterus.

If a woman and a man have unprotected sexual intercourse, sperm that is ejaculated from the man's penis may reach the egg in the fallopian tube. If one of the sperm cells penetrates the egg, the egg is fertilized camera.gif and begins developing.

The egg takes several days to travel down the fallopian tube into the uterus. After it is in the uterus, a fertilized egg usually attaches to (implants in) the lining of the uterus (endometrium). But not all fertilized eggs successfully implant. If the egg is not fertilized or does not implant, the woman's body sheds the egg and the endometrium. This shedding causes the bleeding in a woman's menstrual period camera.gif.

When a fertilized egg does implant, a hormone called human chorionic gonadotropin (hCG) begins to be produced in the uterus. This is the hormone that a pregnancy test measures. It prevents the uterine lining from being shed, so the woman does not have a period. Other signs such as breast changes and nausea occur in a woman's body, also meaning that pregnancy has begun.

    This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

    WebMD Medical Reference from Healthwise

    Last Updated: May 03, 2012
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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