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 that starts on the first day of the mother's last menstrual period.
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, the 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)
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
Low birth weight
Baschat AA, Galan HL. Intrauterine growth restriction. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics Essentials: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2019:chap 33.
Suhrie KR, Tabbah SM. High-risk pregnancies. 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 114.
Review Date 7/13/2021
Updated by: John D. Jacobson, MD, Department of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.