Intrauterine growth restriction (IUGR)



Intrauterine growth restriction

Fetal growth restriction

Failure of the fetus to attain its biologic determined growth potential is associated with increased risk of perinatal mortality and morbidity, as well as adverse neurodevelopment in childhood and long-term risks of cardiovascular, respiratory, and neurological morbidity.

Intrauterine growth restriction refers to a fetus with biometry below a given percentile for gestational age, while small for gestational age refers to newborns with birthweight less than the 10th percentile for gestational age.

Fetal growth restriction (FGR) is the largest contributor to late pregnancy still birth. 


The rate is still birth is 0.8 per thousand births when detected and managed compared with 16.4 per thousand when it is undetected.


Intrauterine growth restriction (IUGR) refers to poor growth of a fetus while in the mother’s womb during pregnancy. 


The causes can be many.


Most often IGR involves poor maternal nutrition or lack of adequate oxygen supply to the fetus.


Approximally 60% of the 4 million neonatal deaths that occur worldwide every year are associated with low birth weight (LBW), caused by intrauterine growth restriction (IUGR), preterm delivery, and genetic abnormalities, demonstrating that under-nutrition is already a leading health problem at birth.


IUGR can result in a baby being small for gestational age (SGA): weight below the 10th percentile for the gestational age.


There are two major categories of IUGR: pseudo IUGR and true IUGR


Pseudo IUGR, the fetus has a birth weight below the tenth percentile for the corresponding gestational age but has a normal ponderal index, subcutaneous fat deposition, and body proportion. 


Pseudo IUGR occurs due to uneventful intrauterine course and can be rectified by proper postnatal care and nutrition.


Such babies are also called small for gestational age.


IUGR is related to pathological conditions which may be either fetal or maternal in origin. 


In addition to low body weight they have abnormal ponderal index, body disproportion, and low subcutaneous fat deposition. 


Some conditions of IUGR are associated with both symmetrical and asymmetrical growth restriction.


In asymmetrical IUGR, there is restriction of weight followed by length. 


In asymmetrical IUGR the head continues to grow at normal or near-normal rates.



In asymmetrical IUGR there is a lack 



of subcutaneous fat leads with a thin and small body out of proportion with the liver. 


Normally at birth the brain of the fetus is 3 times the weight of its liver, but with IUGR, it becomes 5-6 times as big.


Other findings with IUGR include dry, peeling skin and an overly-thin umbilical cord. 


IUGR babies are at increased risk of hypoxia and hypoglycemia, and this type of IUGR is most commonly caused by extrinsic factors that affect the fetus at later gestational ages:


Chronic high blood pressure


Severe malnutrition


Genetic mutations, Ehlers–Danlos syndrome


Symmetrical IUGR is commonly known as global growth restriction..


Symmetrical IUGR indicates the fetus has developed slowly throughout the duration of the pregnancy and was thus affected from a very early stage. 


In symmetrical IUGR the head circumference of such a newborn is in proportion to the rest of the body. 


Most neurons are developed by the 18th week of gestation, therefore the fetus with symmetrical IUGR is more likely to have permanent neurological sequelae. 


Common causes of IUGR include:


Early intrauterine infections, such as cytomegalovirus, rubella or toxoplasmosis


Chromosomal abnormalities




Maternal substance use


Poor weight gain during pregnancy






Maternal smoking


Recent pregnancy


Pre-gestational diabetes


Gestational diabetes


Pulmonary disease


Cardiovascular disease


Kidney disease




Celiac disease 


increases the risk of intrauterine growth restriction by an odds ratio of approximately 2.48


Blood clotting disorder/disease 




Multiple gestation


Uterine malformations


Placental insufficiency


Chromosomal abnormalities


Vertically transmitted infections


Erythroblastosis fetalis


Congenital abnormalities


With IUGR extrinsic to the fetus, by maternal or uteroplacental causes, the transfer of oxygen and nutrients to the fetus is decreased. 


When decreased transfer of oxygen and nutrients to the fetus occurs it causes 


a reduction in the fetus’ stores of glycogen and lipids. 


IUGR often results  in hypoglycemia at birth. 


Secondary polycythemia can occur due to increased erythropoietin production caused by the chronic hypoxemia. 


Hypothermia, thrombocytopenia, leukopenia, hypocalcemia, and bleeding in the lungs often manifest as a result of IUGR.


When the cause of IUGR is intrinsic to the fetus, growth may be restricted due to genetic factors or as a sequela of infection.


IUGR is associated with a wide range of neurodevelopmental disorders.


There is a decrease of the dimension of the white and grey matter in IUGR infants at one year corrected age, compared to at term and preterm infants.


Children with IUGR often exhibit brain reorganization including neural circuitry, that has been linked to learning and memory differences between children born at term and those born with IUGR.


Children born with IUGR had lower IQ, and exhibit other deficits that point to frontal lobe dysfunction.


IUGR infants with brain-sparing show accelerated maturation of the hippocampus which is responsible for memory: such uncharacteristic change leads to development that may compromise other networks and lead to memory and learning deficiencies.


Management of IUGR: 


Bed rest does not improve outcomes and therefore is not typically recommended.


Monitoring techniques: umbilical artery Doppler, has been shown to decrease the risk of morbidity and mortality before and after parturition among IUGR patients.


Umbilical artery Doppler parameters: pulsatility index, resistance index, and end-diastolic velocities, which are measurements of the fetal circulation.


L-arginine has tentative evidence of benefit in reducing intrauterine growth restriction.


IUGR affects 10% of pregnancies, however when corrected for several factors such as low maternal weight it is estimated only around 3% of pregnancies are affected by true IUGR. 


20% of stillborn infants have IUGR. 


Perinatal mortality rates are 4-8 times higher for infants with IUGR, and morbidity is present in 50% of surviving infants.


Intrauterine growth restriction triggers epigenetic responses in the fetus that are otherwise activated in times of chronic food shortage. 


Subsequent exposure to an environment rich in food it may make  IUGR babies prone to metabolic disorders, such as obesity and type II diabetes.




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