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first trimester of pregnancy

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Fetal Development Movie

Alternative Names
early prenatal period, pregnancy, first trimester

Definition

Pregnancy is the process of childbearing. Measured from the start of a woman's last normal menstrual period, or LMP, it usually lasts about 40 weeks, or roughly 9 calendar months.

The first trimester of pregnancy lies between weeks 0 to 13, the second between 13 and 26 weeks, and the third trimester after the 26th week. Although women experience many of the same physical changes during this time, no two pregnancies are alike.

What is the information for this topic?

A woman can learn if she is pregnant within a few weeks after an egg is fertilized during conception. Pregnancy tests check for rising levels of a specific hormone. Home pregnancy tests may be done on urine. Tests done at a lab may use urine or blood.

The fertilized egg is called an embryo for the first 8 weeks. After that it is called a fetus or an unborn child. Its links to the mother appear quite early.

During the first trimester, growth and development of the unborn child inside the mother causes many changes to occur. A woman may notice: Other common signs of early pregnancy in women include: In the unborn child:

By the end of the first trimester, the unborn child is about 4 inches long and weighs just a bit more than 1 ounce. While many pregnancies run into no trouble during this time, problems can occur:

During the first trimester of pregnancy, monitoring may include:
Author:Dr. Karen Wolfe, MBBS, MA
Date Written:04/30/00
Medical Review:Adam Myers, MD
Date Written:10/3/2006
Reviewer:Walt Larimore, MD
Date Reviewed:10/7/2006
Contributors
Potential conflict of interest information for reviewers available on request