Definition of "Intrauterine growth restriction"

Last modified: 10 months

Intrauterine growth restriction (IUGR) is poor growth of a baby while in the mother's womb during pregnancy.

Patient information

What is intrauterine growth restriction ? What a mouthful !
So it's a small baby, caused by some sort of restriction, whilst inside mom's tummy. So it's some sort of bad cause, not just a small bub.

  • SGA, when born
  • Malnourished appearance, including:
    • Thin
    • Pale
    • Loose, dry skin
    • Umbilical cord is often thin and dull, instead of thick and shiny

Patient information

What happens when some sort of bad thing causes bub to be born small?
So it goes without saying that they're small, when born . They might also look like they haven't had enough nutrition, so be thin, pale, dry skin, and their tummy cord might be thin and dull, rather than thick and shiny.


Patient information

What are the causes of some sort of bad thing causing bub to be born small?
So it can be due to mom, bub, or the thing that connects mom and bub. So with mom, she might not be eating right, have low weight, low blood, be using alcohol or smoking, or have some sort of disease relating to pregnancy like high blood sugar, issues with the heart, lungs, kidney, or blood pressure. With the thing that connects mom and bub, there might be preeclampsia, multiple bub's, or some other issues with the womb or placenta. In bub, they may have chromosomal abnormalities, or an infection from mom.

  • If the cause of IUGR is extrinsic (i.e. maternal or uteroplacental), transfer of oxygen and nutrients to the fetus is decreased. This reduces the fetus' stores of glycogen and lipids, often causing hypoglycemia at birth
  • If the cause of IUGR is intrinsic (i.e. fetus itself), growth is restricted due to genetic factors, or as sequelae of infection
  • Asymmetrical IUGR (70%), where restriction is disproportionate. There is sparing of head circumference, called head sparing, because restriction is recent, and neuroprotective physiology has caused a thin/small body disproportionate with head size. This infers the fetus has grown normally in the first 2 trimesters, but encountered difficulties in the 3rd (e.g. due to pre-eclampsia). A lack of subcutaneous fat leads to a thin and small body out of proportion with the head. This is a protective mechanism that has evolved to promote brain development. Other Sx apart from disproportion include dry, peeling skin, and an overly thin umbilical cord. The baby is at increased risk of hypoxia and hypoglycemia. It is most commonly caused by extrinsic factors, that affects the fetus at later gestational ages, including:
    • Chronic hypertension
    • Severe malnutrition
    • Genetic mutations (e.g. Ehlers-Danlos syndrome)
  • Symmetrical IUGR (aka global growth restriction) (22.5%), where restriction is evenly distributed [throughout the body and head], or global growth restriction. This indicates the fetus has developed slowly throughout the entire pregnancy, thus affected from a very early stage. This thus causes head circumference to be proportionate to the body size. Because most neurons are developed by 18 weeks gestation, symmetrical IUGR is likely to cause permanent neurological damage. Causes include:
    • Early intrauterine infections, e.g. cytomegalovirus, rubella, toxoplasmosis
    • Chromosomal abnormalities
    • Anemia
    • Maternal substance abuse (e.g. maternal drinking causing fetal alcohol syndrome)

Patient information

What are the different sorts of bad things causing bub to be born small?
So the small growth can be 1 of 2 sorts. It can either be symmetric, where bub's head and body are both small. Or asymmetric, where bub's head remains big, but the body is small. Where bub is small throughout, it means that this has started from very early in pregnancy, and because most neurons are developed by 18 weeks gestation, it's likely to cause brain problems. So things that cause these are things like early womb infections, chromosomal problems, low blood in mom, or drug abuse by mom. Then there's where the head is normal but the body is small, which means that bub has grown normaly up until the 3rd trimester, where problems have started. It's usually caused by problems outside of bub, like chronic high blood pressure, or severe malnutrition.

  • Fetal palpation, for SGA per McDonald's rule → slow growth
  • U/S (serial growth scans), to check for:
    • Low estimated baby weight → slow growth
    • Low amniotic fluid → insufficient nutrition
    • Doppler flow, for reduced flow between umbilical cord to baby → insufficient nutrition
  • CTG, for HR → fetal wellbeing
  • Maternal weight, for lack of weight gain → growth problem
  • Amniocentesis → infection, chromosomal abnormalities

Patient information

How do you check whether something bad has caused bub to be born small?
You can feel mom's tummy, and feel for a small size for a particular gestational age. You cando ultrasound scans, which can show things like baby weight, amniotic fluid, as well as blood flow in bub's tummy cord. You can do CTG to check for heart rate. You can weigh mom, and check for lack of weight gain in her. You can also test the amniotic fluid, to check for infection or chromosomal abnormalities.

  • IUGR is a fetus that hasn’t reached its growth potential because of genetic or environmental factors as calculated by symphysis-fundal height measurement or U/S, cf. SGA which is constitutionally small but otherwise normal
  • Prevention, because the earlier the problem begins, the greater the risks to the baby. Also:
    • Improving maternal nutrition
    • Bed rest, to help improve circulatio in the fetus
  • Early IOL, but only if a cause has been Dx, and is a risk to the health of the fetus
  • If the cause of IUGR is extrinsic to the fetus (maternal or uteroplacental):
    • Hypoglycemia at birth, as the transfer of oxygen and nutrients to the fetus is decreased, reducing the fetus’ stores of glycogen and lipids
    • Polycythemia, due to increased erythropoietin production, due to chronic hypoxemia
    • Hypothermia
    • Thrombocytopenia
    • Leukopenia
    • Hypocalcemia
    • Pulmonary hemorrhage
    • ​May be more prone to metabolic disorders, e.g. obesity and T2DM, if the offspring actually develops in an environment rich in food, as according to the thrifty phenotype theory, IUGR restriction triggers epigenetic responses in the fetus that are otherwise activated in times of chronic food shortage
  • If the cause of IUGR is intrinsic to the fetus:
    • Growth is restricted due to genetic factors
    • Sequelae of infection

Patient information

What bad things can happen due to something bad that has caused bub to be born small?
So if the cause is from bub themselves, the problem is restricted to the genetic problem, or if it's an infection, whatever problem the infection causes. However, if the problem is outside of bub themselves, they can be born with low blood glucose, increased hemoglobin in blood to offset for low oxygen. They can also be more prone to metabolic disorders.

  • Can result in baby being Small for Gestational Age (SGA, i.e. weight<10th percentile for gestational age)
  • At the end of pregnancy, can result in low birth weight (LBW)
  • Babies who've been starved in utero tend to be hungry, and feed enthusiastically to gain weight, so they can expect normal or only slightly reduced stature
  • If there is slow head growth <26 weeks, they may show significant developmental delay at 4yo
  • Associated with impaired executive cognitive function as a young adult
  • Extremely LBW implies high risk of mortality and morbidity too
  • LBW <2.5kg have 3x risk of death due to CAD later in life, and increased risk of HTN, type 2 diabetes, and autoimmune thyroid disease
  • Affects 6.5% of pregnancies
  • 20% of stillborn infants have IUGR
  • Perinatal mortality rates are 6 times higher for infants with IUGR, and morbidity is present in 50% of surviving infants
  • At least 60% of neonatal deaths occur worldwide per annum, are associated with low birth weight (LBW), caused by intrauterine growth restriction (IUGR), preterm delivery, and genetic/chromosomal abnormalities
  • Asymmetrical IUGR is more common (70%) than symmetrical IUGR (23%)
See also
  • SGA (IUGR is a cause of SGA)

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Amanda Gordon

Female Psychologist
Armchair Psychology - Edgecliff NSW

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