• Clinical science

Intrauterine growth restriction


Intrauterine growth restriction (IUGR) is defined as lower than normal fetal growth characterized by an estimated fetal weight below the 10th percentile for a given gestational age. There are two types of IUGR: asymmetrical and symmetrical. Asymmetrical IUGR is caused by extrinsic influences (most commonly placental insufficiency) that affect the fetus in the later stages of gestation and symmetrical IUGR is caused by intrinsic influences (e.g., early intrauterine infections, aneuploidy) that affect the fetus in the early stages of gestation. IUGR is diagnosed with serial ultrasound, which demonstrates decreased fetal growth and oligohydramnios. Typical manifestations of asymmetrical IUGR are a normal fetal head size with a disproportionately small body and limbs, while symmetrical IUGR typically manifests with a global growth restriction of the head and body and can lead to an increased risk of neurologic sequelae. Treatment should address the underlying cause. Regular nonstress test (NST), contraction stress test (CST), and biophysical profile (BPP) are recommended to closely monitor fetal status and placental development. Labor induction or cesarean section should be considered if the infant is close to term or if there are signs of nonreassuring fetal status.


Maternal causes

Uteroplacental causes

Fetal factors

Asymmetrical IUGR is the most common manifestation of IUGR (∼ 70%), has a late onset, and is usually due to maternal systemic disease (e.g., hypertension) that results in placental insufficiency. Symmetrical IUGR is less common (∼ 30%) and is usually due to a genetic disorder (e.g., aneuploidy), congenital heart disease, or early intrauterine TORCH infection that affects the fetus early in gestation.



Epidemiological data refers to the US, unless otherwise specified.


Asymmetrical IUGR

Caused by extrinsic factors, which affect the fetus in the later stages of gestation (i.e., third trimester).

  • Impaired function of the uteroplacental unit (see placental function) → insufficient transplacental delivery of oxygen and nutrients to the fetus and impaired return of carbon dioxide and fetal metabolic waste products from the fetus to the mother's circulation

Symmetrical IUGR

Caused by intrinsic factors (e.g., genetic abnormalities, infections), which affect the fetus in the early stages of gestation.




Clinical features

Fetal signs

  • Small for gestational age (or with a birth weight below 10th percentile) [3]
  • Decreased or absent fetal movements [9]
  • Asymmetrical IUGR: disproportionate growth restriction
    • The dimensions of the head are normal while the body and limbs are thin and small.
  • Symmetrical IUGR: global growth restriction
    • The entire body is proportionally small.
    • The circumference of the head is proportional to the rest of the fetal body.
    • ↑ Risk of neurologic sequelae [10]

Maternal signs


We list the most important complications. The selection is not exhaustive.