Skip to Content
Gestational age is the number of weeks and days a fetus has
developed since the beginning of the pregnancy, or gestation. A pregnancy is
formally considered as beginning on the first day of the mother's last
menstrual period (LMP).
An infant born before 37 completed weeks' gestation is considered
premature. A premature infant is often referred to in terms of gestational age
(a "30-weeker"), which implies a particular point of development at birth. After
a premature infant is born, the gestational age is also referred to as the
infant's postconceptional age. This figure is useful for estimating an infant's
growth and development until some time around the due date (40 weeks).
Gestational age is also estimated by using ultrasound measurements of the fetus combined with the dates of first
fetal heart tones and other developmental milestones. After the infant is born,
there are a variety of characteristics that can be used to estimate the
It is possible for gestational age to be inaccurate by up to 2
weeks, even with an accurate LMP date confirmed by other tests.
Current as of:
May 30, 2016
Sarah Marshall, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & Adam Husney, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology
To learn more about Healthwise, visit Healthwise.org.
© 1995-2016 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
© Copyright 2016 Rush-Copley Medical Center • 2000 Ogden Avenue; Aurora, IL 60504
Main: 630-978-6200 • Physician Referral & Information: 630-978-6700 or 866-4COPLEY (866-426-7539)