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There is often confusion in dating a pregnancy and the terms that are used. Two primary terms are used, and neither of them is the traditional “nine months.”

Gestational Age: Medical professionals commonly use gestational age, which calculates the weeks of pregnancy based on the first day of your last menstrual period (LMP). Ultrasound also calculates the gestational age. This method of dating assumes that conception occurs 14 days after the first day of your last period.

Fetal Age: This is the actual age of the pregnancy since conception. Because the ability to more accurately date a pregnancy with ultrasound is a fairly recent development, this more exact measurement is not commonly used.

Most publications that discuss fetal development will use gestational age as the benchmark. If it uses fetal age it will state “since conception.” Ultrasound reports calculate the gestational age and not the more exact fetal age which helps to keep dating consistent.

Using gestational age, a pregnancy last 40 weeks instead of the actual 38.

If you’re confused about the dating of your pregnancy, don’t hesitate to ask your medical provider.

The information provided here is general in nature.  It is not a substitute for a consultation with a medical professional. Before any medical procedure, it is imperative that you discuss your personal medical history, risks, and concerns with your doctor. If you have questions during or after a procedure, your doctor should be immediately contacted. Avenue Women’s Center is not an emergency center.  If you are experiencing severe symptoms, such as bleeding and/or pain, seek immediate medical attention.  Contact your physician, go to an emergency room, or call 911.