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Small-for-Gestational-Age (SGA) Newborn

(Intrauterine Growth Restriction)


Arcangela Lattari Balest

, MD, University of Pittsburgh, School of Medicine

Last full review/revision Apr 2021| Content last modified Sep 2022

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 or has used drugs, smoked, or consumed 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 Gestational age Problems in newborns may develop Before birth while the fetus is growing During labor and delivery After birth About 10% of newborns need special care after birth due to prematurity, problems... read more refers to how far along the fetus is. The gestational age is 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 published growth charts or computer apps to evaluate babies at other gestational ages.

Causes of SGA Newborn

Most newborns who are moderately small for gestational age are normal babies who just happen to be on the smaller side. However, some have had their growth restricted by various factors. 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: Only weight is affected.

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.

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 SGA babies.

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

Pregnancy risk factors

Fetal risk factors

Symptoms of SGA Newborn

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

Immediate complications

During pregnancy, growth-restricted fetuses are at increased risk of miscarriage Miscarriage A miscarriage is the loss of a fetus due to natural causes before 20 weeks of pregnancy. Miscarriages may occur because of a problem in the fetus (such as a genetic disorder or birth defect)... read more or stillbirth Stillbirth Stillbirth is death of a fetus after 20 weeks of pregnancy. Pregnancy complications are problems that occur only during pregnancy. They may affect the woman, the fetus, or both and may occur... read more . At birth, small-for-gestational-age newborns who are born full term do not have the complications related to organ system immaturity that premature newborns of similar size have. They are, however, at increased risk of the following problems:

Long-term complications

Recent studies suggest that intrauterine growth restriction increases the likelihood of problems during adulthood, including heart disease, high blood pressure, and stroke.

Diagnosis of SGA Newborn

  • 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 the 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 diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... 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 baby. Doctors measure the baby'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.

Prognosis of SGA Newborn

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 perinatal 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.

Infants whose growth was restricted because their mother used alcohol while pregnant are likely to have long-term developmental and behavioral problems.

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

Treatment of SGA Newborn

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

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