Gestation is the period of time between conception and birth. During this time, the baby grows and develops inside the mother's womb.
If the baby's gestational age findings after birth match the calendar age, the baby is said to be appropriate for gestational age (AGA).
AGA babies have lower rates of problems and death than babies that are small or large for their gestational age.
Gestational age is the common term used during pregnancy to describe how far along the pregnancy is. It is measured in weeks, from the first day of the woman's last menstrual cycle to the current date. A normal pregnancy can range from 38 to 42 weeks.
Gestational age can be determined before or after birth.
- Before birth, your health care provider will use ultrasound to measure the size of the baby's head, abdomen, and thigh bone. This provides a view on how well the baby is growing in the womb.
- After birth, gestational age can be measured by looking at the baby. Weight, length, head circumference, vital signs, reflexes, muscle tone, posture, and the status of the skin and hair are assessed.
Graphs are available showing the upper and lower normal limits for different gestational ages, from around 25 weeks of gestation through 42 weeks.
The wait for full-term infants that are born AGA will most often be between 2,500 grams (about 5.5 lbs or 2.5 kg) and 4,000 grams (about 8.75 lbs or 4 kg).
Fetal age; Gestation; Development - AGA; Growth - AGA; Neonatal care - AGA; Newborn care - AGA
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Nock ML, Olicker AL. Tables of normal values. In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin's Neonatal-Perinatal Medicine. 11th ed. Philadelphia, PA: Elsevier; 2020:Appendix B, 2028-2066.
Richards DS. Obstetric ultrasound: imaging, dating, growth, and anomaly. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 9.
Review Date 10/2/2019
Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.