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Small for gestational age (SGA)

Small for gestational age means that a fetus or an infant is smaller or less developed than normal for the baby's gender 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.

Causes for SGA fetus may include:

  • Genetic diseases
  • Inherited metabolic diseases
  • Chromosome anomalies
  • Multiple gestations (twins, triplets, etc)

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


Baschat AA, Galan HL. Intrauterine growth restriction. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 33.

Carlo WA. The high-risk infant. In: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 97.

Review Date 8/26/2017

Updated by: Peter J Chen, MD, FACOG, Associate Professor of OBGYN at Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.