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Gestational Age Determination
Overview & Description
Gestational age determination involves procedures and tests used to check the age of a fetus during pregnancy.
Who is a candidate for the procedure?
Once a woman learns that she is pregnant, it is important to find out how far along she is in the pregnancy. Knowing the age of the fetus is key to good health care during pregnancy. Traditionally, the due date was based on the following:
All of this is still part of routine obstetrical care. However, these methods are very unreliable for some groups of women, such as:
How is the procedure performed?
There are several methods for determining gestational age. A pregnancy ultrasound uses sound waves to examine and measure the fetus. Undergoing an ultrasound procedure early during the first trimester allows a more accurate due date. Later, ultrasounds tell more about the growth of the fetus and the placenta.
Some ultrasound measurements are as follows:
The following ultrasound measurements are used less often:
The size of the woman's uterus is also used to determine gestational age. During the first trimester, the length of a pregnancy can be determined by a pelvic exam. At 8 weeks, the uterus is felt just at the pubic bone. At 12 weeks, it grows over the pubic bone into the abdomen. At 20 weeks, the top of the uterus lies at the level of the belly button. After that point, it is measured in centimeters. Each centimeter corresponds to the week of pregnancy. Twenty-six centimeters, for example, equals 26 weeks gestation. If there is more than one fetus, this calculation does not apply.
Other methods for determining the age of the fetus include the following:
Preparation & Expectations
What happens right after the procedure?
The woman can go home immediately after a pregnancy ultrasound or any of the other procedures.
Home Care and Complications
What happens later at home?
The woman will not notice any effects at home following the ultrasound or other procedure.
What are the potential complications after the procedure?
There are no complications from a pregnancy ultrasound or the other procedures. As always, any new or worsening symptoms should be reported to the healthcare provider.
Attribution
Author:Eva Martin, MD
Date Written:
Editor:Ballenberg, Sally, BS
Edit Date:08/13/01
Reviewer:Carlos Herrera, MD
Date Reviewed:08/14/01