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Normal Pregnancy

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Gestational age

Definition

Gestation is the period of time between conception and birth. During this time, the baby grows and develops inside the mother's womb.

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.

Infants born before 37 weeks are considered premature. Infants born after 42 weeks are considered postmature.

Information

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's weight, length, head circumference, vital signs, reflexes, muscle tone, posture, and the condition of the skin and hair.

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.

The weight for full-term infants that are born AGA will most often be between 2,500 grams (about 5.5 pounds [lbs] or 2.5 kilograms [kg]) and 4,000 grams (about 8.8 lbs or 4 kg).

• Infants weighing less are considered small for gestational age (SGA).

• Infants weighing more are considered large for gestational age (LGA).

References

Ball JW, Dains JE, Flynn JA, Solomon BS, Stewart RW. Growth and nutrition. In: Ball JW, Dains JE, Flynn JA, Solomon BS, Stewart RW, eds. Siedel's Guide to Physical Examination. 10th ed. St Louis, MO: Elsevier; 2023:chap 8.

Benson CB, Doubilet PM. Fetal measurements: normal and abnormal fetal growth and assessment of fetal well-being. In: Rumack CM, Levine D, eds. Diagnostic Ultrasound. 6th ed. Philadelphia, PA: Elsevier; 2024:chap 43.

Graham GM, Park JS, Norwitz ER. Antepartum fetal assessment and therapy. In: Chestnut DH, Wong CA, Tsen LC, et al, eds. Chestnut's Obstetric Anesthesia: Principles and Practice. 6th ed. Philadelphia, PA: Elsevier; 2020:chap 6.

Goyal NK. The newborn infant. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 113.

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.

Simmons RA. Abnormalities of fetal growth. In: Gleason CA, Sawyer T, eds. Avery's Diseases of the Newborn. 11th ed. Philadelphia, PA: Elsevier; 2024:chap 4.

Review Date: 11/6/2023

Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.