As soon as pregnancy is determined, the woman’s first concern is to determine when the baby is due. The due date is called the Estimated Date of Confinement or EDC. There are several means of determining the EDC including Nagele’s rule, fundal height, and the use of a gestational wheel.
Nagele’s Rule
• It is the most common tool used to determine EDC.
• After determining the first day of the last menstrual period, the examiner would count back 3 months and add 7 days. For example, if the first day of the last menstrual period was September 1, the examiner would subtract 3 months (9 3 6) and add 7 days. The sixth month is June, so the due date would be June 8.
• Inaccurate determinations occur when the date of the last menstrual period cannot be recalled. These are frequently associated with delays in seeking medical attention.
• EDC may be incorrectly defined when the woman missed a cycle before conceiving or had vaginal bleeding after conception. Some women will have a “light period” after conceiving while others have been known to continue to have cycles well into the pregnancy.
Fundal Height Measurement
• In fundal height measurement, the examiner measures the distance from the symphysis pubis to the top of the fundus.
• Measured in centimeters, the fundal height measurement corresponds well with the fetal age in the second and third trimester.
• Women carrying more than one fetus will appear to be further along in their pregnancy with this EDC determination.
• In situations with intrauterine growth retardation in the fetus or oligohydramnios (less than normal amounts of amniotic fluid), the pregnancy may be incorrectly dated as well.
The Gestation Wheel
• It is an easy to use tool to assist the practitioner in determining EDC.
• Since the system utilizes the first day of the last menstrual period, this method has the same difficulties as Nagele’s rule.
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