Small for gestational age means that a fetus or an infant is smaller or less developed than normal for the baby's sex and gestational age. Gestational age is the age of a fetus or baby counting from the first day of the mother's last menstrual period.
Information
Ultrasound is used to find out if a fetus is smaller than normal for their age. This condition is called intrauterine growth restriction. The most common definition of small for gestational age (SGA) is a birth weight that is below the 10th percentile. At the time of the ultrasound exam, your health care provider may use other findings, such as the amount of amniotic fluid surrounding the baby, to further understand the baby's condition.
Causes for SGA fetus may include:
- Genetic diseases
- Inherited metabolic diseases
- Chromosome anomalies
- Multiple gestations (twins, triplets, and more)
- Abnormal placenta
- High blood pressure
A developing baby with intrauterine growth restriction will be small in size and can have problems such as:
- Increased red blood cells
- Low blood sugar
- Low body temperature
Alternative Names
Low birth weight
References
Balest AL, Riley MM, O'Donnell B, Zarit JS. Neonatology. In: Zitelli BJ, McIntire SC, Nowalk AJ, Garrison J, eds. Zitelli and Davis' Atlas of Pediatric Physical Diagnosis. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 2.
Baschat AA, Su EJ, Galan HL. Fetal growth restriction. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 9th ed. Philadelphia, PA: Elsevier; 2025:chap 30.
Triebwasser JE, Dolin CD. High-risk pregnancies. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 116.
Review Date 8/18/2025
Updated by: LaQuita Martinez, MD, Department of Obstetrics and Gynecology, Emory Johns Creek Hospital, Alpharetta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.