Difference Between IUGR and SGA

Intrauterine Growth Restriction (IUGR) and Small for Gestational Age (SGA) are two terms used to describe fetal growth problems during pregnancy. While they may seem similar, there are important differences between the two. Understanding the difference between IUGR vs. SGA can help healthcare providers diagnose and manage these conditions, which are associated with an increased risk of morbidity and mortality.

What is IUGR?

IUGR is intrauterine growth retardation or restriction, and it is the condition in which the growth of the fetus in the uterus is poor and restricted. The key feature of IUGR is the appearance of a malnourished infant at birth regardless of their size.


A fetus with IUGR will often be smaller than usual for its age of gestation in utero, but regardless of how much smaller they may be in size, these infants will look malnourished when born and the head may appear larger than normal compared with the rest of the body. These babies also often have dry and loose skin, a small abdomen and the umbilical cord appears thin and small in size. Some children have Russell-Silver Syndrome which is IUGR resulting in specific features such as having a large head, and a triangular shape to the face.


A fetus that has IUGR can be detected by the doctor measuring the distance between the fundus of the uterus and the pubic bone. The value obtained should be in accordance with the gestational time period that has passed and should fall within a specific size range. If the value is lower than expected, then IUGR may be suspected. Doppler can be done to measure blood flow in the uterine arteries and if these values are reduced, then IUGR may be present. Ultrasounds taken over a period of time can be done to measure the size of the baby’s abdomen and head and compare these with normal growth measurements for the particular weeks of pregnancy that has elapsed. Only measurements taken over time can indicate abnormal growth patterns. Small growth values and low amounts of amniotic fluid can indicate IUGR.


The most common causative factors of IURG are problems of the placenta or uterus or due to a problem with the formation of the fetus. Researchers have found that the transport of nutrients such as amino acids through the placenta is greatly decreased in the case of fetuses that have IUGR. Decreased placental blood flow is also a factor and if the woman is carrying multiple fetuses. There are several other causes of IUGR, including a woman who uses drugs or alcohol during pregnancy, has anemia, diabetes, kidney disease, or does not gain enough weight during pregnancy. Genetic abnormalities or infections in the uterus can also cause IUGR. Infections that can cause IURG include toxoplasma, cytomegalovirus, rubella, toxoplasma, syphilis, herpes, and malaria


There is an increased mortality rate of fetuses and babies that have IUGR, and many of the complications depend on the cause of the condition. Some fetuses may die in utero from the condition. At birth, the IUGR infant may aspirate meconium or experience perinatal asphyxia. They may also have hypoglycemia or hypothermia. Jaundice and polycythemia may also occur at birth.

What is SGA?

SGA is Small for Gestational Age and describes the condition in which the size of a developing fetus is below normal (less than the 10th percentile) or two standard deviations below what is average, for their age of gestation.


Physically these infants when born appear to be normal in appearance except for appearing thin and having little fat and muscle tissue. Sometimes the face can appear somewhat sunken. The umbilical cord may also often not be thick or large but appears smaller than normal.


The condition of SGA in a fetus is best diagnosed using a combination of clinical measurements and ultrasound measures of fetal size. Measurement of size from the fundus to the pubic bone should be done on the mother. An ultrasound can show the size of the head, abdomen and entire body. These various measures can then be compared with the time of gestation and if the value falls below 10% of what is expected for that time of development, then SGA can be confidently diagnosed.


The complications present in an SGA baby are similar to those of an IUGR infant. Problems such as meconium aspiration or asphyxia can occur at birth, especially if the SGA is due to IUGR. Other complications that may arise include polycythemia and hypoglycemia. Hypothermia may arise at birth as well due to the child being SGA.

Treatment and prevention

Supportive care is given to the baby who is born SGA, and any complications are treated accordingly. Although not all causes can be prevented, the best approach to try to prevent the condition is for the mother to stay healthy and to keep doctor’s appointments while pregnant.

Differences: IUGR vs. SGA

Firstly, it is important to understand what is meant by fetal growth. Fetal growth is the increase in weight, length, and head circumference of a developing fetus during pregnancy. Fetal growth is influenced by various factors, including maternal nutrition, maternal health, genetics, and environmental factors.

Intrauterine Growth Restriction (IUGR) refers to a fetal growth problem that is due to an underlying pathological process. This means that the fetus is not growing properly due to some form of disease or disorder. IUGR can occur due to a number of reasons, including maternal hypertension, preeclampsia, gestational diabetes, placental abnormalities, fetal infections, and chromosomal abnormalities.

In contrast, Small for Gestational Age (SGA) refers to a fetus that is smaller than expected for its gestational age. This means that the fetus is not growing at the expected rate, but there is no underlying pathological process. SGA can occur due to various reasons, such as maternal malnutrition, smoking, drug abuse, placental insufficiency, and fetal genetic disorders.

While IUGR and SGA are different in their underlying causes, they share some similarities in terms of their clinical presentation. In both conditions, the fetus may have a low birth weight, small size, and may be at increased risk of perinatal complications. These complications can include preterm birth, hypoxia, meconium aspiration, and neonatal mortality.

Diagnosis of IUGR vs. SGA requires accurate assessment of fetal growth. This is typically done using ultrasound measurements of fetal weight, head circumference, and abdominal circumference. The ultrasound measurements are compared to population standards to determine whether the fetus is growing at an appropriate rate for its gestational age. If the fetal growth is below the 10th percentile, the fetus is considered to be small for gestational age (SGA). If the fetal growth is below the 3rd percentile or if there is evidence of abnormal fetal blood flow, the fetus is considered to have intrauterine growth restriction (IUGR).

Management of IUGR vs. SGA depends on the underlying cause and the severity of the fetal growth problem. In cases of IUGR, management typically involves close monitoring of fetal growth and wellbeing, and delivery may be recommended if there is evidence of fetal distress or compromised fetal health. In cases of SGA, management typically involves monitoring fetal growth and wellbeing and may include interventions to improve maternal nutrition, reduce maternal stress, and manage any underlying maternal health problems.

The following table highlights the major differences between IUGR and SGA −





IUGR is when the growth of a fetus is retarded or restricted in utero.

SGA is when the fetus is smaller than normal for its gestational age.


In IUGR the babies always look as though they have been malnourished.

In SGA, babies do not always appear malnourished.


An IUGR fetus is diagnosed by measurement, ultrasound and noting Doppler flow through the blood vessels.

An SGA fetus is diagnosed by measurement and ultrasound.


IUGR is based on more than one measurement to indicate growth patterns.

SGA is based on one measurement taken at one point in time.

Growth rate in utero

A fetus with IUGR always shows slower than normal growth in the uterus.

An SGA baby does not always show slower than average growth.

Birth weight

The birth weight of a baby with IUGR is not always lower than normal.

The birth weight of an SGA baby is always lower than normal.

Pathological condition

The IUGR condition is always pathological; it is always due to a problem in utero.

The SGA condition is not always due to a problem and may be due to a very small size mother.


In summary, IUGR and SGA are both fetal growth problems, but they differ in their underlying causes. IUGR is due to an underlying pathological process, while SGA is a result of a fetus not growing at the expected rate. Accurate diagnosis and management of these conditions are important to reduce the risk of adverse perinatal outcomes.

Healthcare providers should be aware of the differences between IUGR vs. SGA to provide appropriate care to pregnant women and their fetuses.

Updated on: 26-Apr-2023


Kickstart Your Career

Get certified by completing the course

Get Started