Intrauterine growth restriction (IUGR) refers to poor growth of a baby while in the mother's womb during pregnancy. The causes can be many, but most often involve poor maternal nutrition or lack of adequate oxygen supply to the fetus.

At least 60% of the 4 million neonatal deaths that occur worldwide every year are associated with low birth weight (LBW)

Low birth weight

Low birth weight is defined as a birth weight of a liveborn infant of less than 2,500 g. regardless of gestational age-Causes:LBW is either the result of preterm birth or of the infant being small for gestational age , or a combination of...

, caused by intrauterine growth restriction (IUGR), preterm delivery, and genetic/chromosomal abnormalities , demonstrating that under-nutrition is already a leading health problem at birth.

Terminology

The term IUGR is not synonymous with Small for Gestational Age

Small for gestational age

Small for gestational age babies are those who are smaller in size than normal for the baby's sex and gestational age, most commonly defined as a weight below the 10th percentile for the gestational age.-Terminology:...

 (SGA). SGA refers to a birth weight

Birth weight

Birth weight is the body weight of a baby at its birth.There have been numerous studies that have attempted, with varying degrees of success, to show links between birth weight and later-life conditions, including diabetes, obesity, tobacco smoking and intelligence.-Determinants:There are...

 that is below the 10th percentile

Percentile

In statistics, a percentile is the value of a variable below which a certain percent of observations fall. For example, the 20th percentile is the value below which 20 percent of the observations may be found...

 for gestational age. Not all fetuses with IUGR are classified as SGA, and vice versa. IUGR is used to describe a pattern of intrauterine fetal growth that deviates from expected norms, whereas SGA is a category assigned based on birth weight.

Symmetrical vs. asymmetrical

There are 2 major categories of IUGR: symmetrical and asymmetrical.

Asymmetrical IUGR is more common. In asymmetrical IUGR, there is restriction of weight followed by length. The head continues to grow at normal or near-normal rates (head sparing). This is a protective mechanism that may have evolved to promote brain development. This type of IUGR is most commonly caused by extrinsic factors that affect the fetus at later gestational ages.

Symmetrical IUGR is less common and is more worrisome. This type of IUGR usually begins early in gestation

Gestation

Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....

. Since most neurons are developed by the 18th week of gestation, the fetus with symmetrical IUGR is more likely to have permanent neurological sequela

Sequela

A sequela) is a pathological condition resulting from a disease, injury, or other trauma.Chronic kidney disease, for example, is sometimes a sequela of diabetes, and neck pain is a common sequela of whiplash or other trauma to the cervical vertebrae. Post-traumatic stress disorder may be a...

.

Maternal

• prepregnancy weight and nutritional status
• poor weight gain during pregnancy
• recent pregnancy
  Pregnancy
  Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
  
  
• poor nutrition
• alcohol and/or drug use
• smoking
• pulmonary disease
• cardiovascular disease
• renal disease
• diabetes
• anemia
  Anemia
  Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
  
  
• hypertension
  Hypertension
  Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
  
  

Uteroplacental

• preeclampsia
• multiple gestation
  Multiple birth
  A multiple birth occurs when more than one fetus is carried to term in a single pregnancy. Different names for multiple births are used, depending on the number of offspring. Common multiples are two and three, known as twins and triplets...
  
  
• uterine
  Uterus
  The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
  
   malformations

Pathophysiology

If the cause of IUGR is extrinsic to the fetus (maternal or uteroplacental), transfer of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and nutrients to the fetus is decreased. This causes a reduction in the fetus’ stores of glycogen

Glycogen

Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

 and lipids. This often leads to hypoglycemia

Hypoglycemia

Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...

 at birth. Polycythemia

Polycythemia

Polycythemia is a disease state in which the proportion of blood volume that is occupied by red blood cells increases...

 can occur secondary to increased erythropoietin

Erythropoietin

Erythropoietin, or its alternatives erythropoetin or erthropoyetin or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production...

 production caused by the chronic hypoxemia

Hypoxemia

Hypoxemia is generally defined as decreased partial pressure of oxygen in blood, sometimes specifically as less than or causing hemoglobin oxygen saturation of less than 90%.-Distinction from anemia and hypoxia:...

. Hypothermia

Hypothermia

Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...

, thrombocytopenia

Thrombocytopenia

Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...

, leukopenia

Leukopenia

Leukopenia is a decrease in the number of white blood cells found in the blood, which places individuals at increased risk of infection....

, hypocalcemia, and pulmonary hemorrhage are often results of IUGR.

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

Outcomes and clinical significance

IUGR affects 3-10% of pregnancies. 20% of stillborn

Stillbirth

A stillbirth occurs when a fetus has died in the uterus. The Australian definition specifies that fetal death is termed a stillbirth after 20 weeks gestation or the fetus weighs more than . Once the fetus has died the mother still has contractions and remains undelivered. The term is often used in...

 infants have IUGR. Perinatal mortality rate

Mortality rate

Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

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