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Small-for-Gestational-Age (SGA) Newborns

(Intrauterine Growth Restriction)


Arcangela Lattari Balest

, MD, University of Pittsburgh, School of Medicine

Reviewed/Revised Jan 2024

A newborn who weighs less than 90% of newborns of the same gestational age at birth (below the 10th percentile) is considered small for gestational age.

  • Newborns may be small because their parents are small, the placenta did not function normally, or the mother has a medical disorder, has taken certain medications, or has used illicit drugs, tobacco, or alcohol during the pregnancy.

  • Unless they are born with an infection or have a genetic disorder, most small-for-gestational-age newborns have no symptoms and do well.

  • Some small newborns remain small as adults.

Gestational age refers to the number of weeks of pregnancy. The gestational age is determined by counting the number of weeks between the first day of the mother's last menstrual period and the day of delivery. This time frame is often adjusted according to other information doctors receive, including the results of early ultrasound scans, which give additional information regarding the gestational age. A baby is estimated to be due (the due date) at 40 weeks of gestation.

At a gestational age of 40 weeks, boys who weigh less than about 6 pounds 9 ounces (3 kilograms) are small for gestational age. Girls who weigh less than about 6 pounds 3 ounces (2.8 kilograms) are small for gestational age. Doctors use growth charts to evaluate babies at other gestational ages.

Causes of SGA Newborns

Most newborns who are moderately small for gestational age are healthy babies who just happen to be on the smaller side. However, some are small because their growth in the womb was restricted by various factors. Growth restriction is when a baby in the womb (a fetus) does not grow as expected.

Growth restriction can be classified as

  • Symmetric: The newborn is proportionately small, that is, its weight, length, and head size are similarly low or small.

  • Asymmetric: Weight, length, or head size are not equally affected (for example, head size may continue to grow as expected, but weight or length may be lower than expected).

In symmetric growth restriction, the cause probably occurred early in the pregnancy when it would affect all of the cells in the newborn's body. Asymmetric growth restriction probably results from problems that occur later in pregnancy because some tissues develop sooner than others and not all would be affected equally.

Not all infants whose growth was restricted in the womb are small for gestational age.

Risk factors for growth restriction include those involving the mother's underlying health, and those involving the pregnancy and/or the fetus.

Maternal risk factors

The risk of having a small-for-gestational-age (SGA) baby is increased for mothers who are very young or very old or who have had other babies who were SGA.

Medical disorders in the mother that increase the risk of having an SGA baby include

Pregnancy risk factors

Fetal risk factors

Symptoms of SGA Newborns

Despite their size, small-for-gestational-age (SGA) newborns usually look and act similar to normal-sized newborns of similar gestational age. Some SGA newborns appear thin and have less muscle mass and fat, and some have sunken facial features. The umbilical cord can appear thin and small.

Immediate complications

Long-term complications

Infants with a history of intrauterine growth restriction may have an increased likelihood of problems during adulthood, including heart disease, high blood pressure, and stroke.

Diagnosis of SGA Newborns

  • Before birth, measurement of the uterus and ultrasonography

  • After birth, assessment of gestational age and size and weight of the baby

During pregnancy, doctors measure the distance on a woman's abdomen from the top of the pubic bone to the top of the uterus (fundus). This measurement, called a fundal height measurement, corresponds roughly with the number of weeks of pregnancy. For example, the normal fundal height for a woman who is 32 weeks pregnant is about 30 to 34 centimeters. If the measurement is low for the number of weeks, the fetus may be smaller than expected.

Ultrasonography Ultrasonography Prenatal testing for genetic disorders and birth defects involves testing a pregnant woman or fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including... read more can be done to assess the size of the fetus and estimate the weight of the fetus to confirm the diagnosis of small for gestational age. Ultrasonography may also be helpful in establishing the cause of the growth restriction and how it has affected the fetus. Depending on the findings, doctors may do genetic testing or magnetic resonance imaging (MRI) to determine the underlying cause.

After birth, small for gestational age is diagnosed by assessing the gestational age and the weight of the newborn. Doctors measure the newborn's length Length and Height Physical growth refers to an increase in body size (length or height and weight) and in the size of organs. From birth to about age 1 or 2 years, children grow rapidly. After this rapid infant... read more and head circumference Head Circumference Physical growth refers to an increase in body size (length or height and weight) and in the size of organs. From birth to about age 1 or 2 years, children grow rapidly. After this rapid infant... read more to categorize the growth restriction as symmetric or asymmetric. Diagnostic tests, including ultrasonography, x-rays, MRI, tests for infection, blood tests, and genetic tests, may be needed to find the cause of the growth restriction.

Treatment of SGA Newborns

  • Treatment of underlying causes and complications

There is no specific treatment for small-for-gestational-age newborns, but underlying conditions and complications are treated as needed. Growth hormone injections are sometimes given to certain SGA infants who remain quite small at 2 to 4 years of age. This treatment must be given for several years and must be considered on a case-by-case basis.

All pregnant people should receive good prenatal care and should avoid alcohol, tobacco, and illicit drugs (such as cocaine and heroin) while pregnant.

Prognosis for SGA Newborns

Prognosis varies greatly depending on what caused the infant to be small for gestational age and whether complications developed.

Infants who have a moderately low birthweight usually do well unless they have an infection, genetic disorder, or birth asphyxia. Most catch up their growth during the first year of life and have a normal adult height.

Infants who are particularly small because of illness in the mother are at risk of complications but usually do well. Some small babies remain small as adults and others are within the normal range.

The outcome for SGA infants exposed to illicit drugs during pregnancy is complicated. It is difficult to predict the prognosis because pregnant people who use illicit drugs often have other social and economic problems that affect their child's development.

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