Small for gestational age is a term used to describe babies who are smaller than usual for the number of weeks of pregnancy. These babies have birth weight below the 10th percentile. This means they are smaller than many other babies of the same gestational age. Many babies normally weigh more than 5 pounds, 13 ounces by the 37th week of pregnancy. Babies born weighing less than 5 pounds, 8 ounces are considered low birth weight.


Some babies are small because their parents are small. But most babies who are small for gestational age have growth problems that happen during pregnancy. Many of these babies have a condition called intrauterine growth restriction. This happens when the unborn baby doesn’t get the nutrients and oxygen needed to grow and develop organs and tissues. This can begin at any time in pregnancy.

Growth restriction early in pregnancy (early onset) happens because of chromosome problems in the baby. It also happens because of disease in the mother,or severe problems with the placenta. Growth restriction is called late onset if it happens after week 32 of the pregnancy. It is usually related to other problems.

Risk Factors

When the unborn baby doesn’t get enough oxygen or nutrients during pregnancy, the baby’s body and organs don't grow as much as they should. Some of the problems that cause babies to be small for gestational age limit how much blood flows through the placenta. This can cause the baby to get less oxygen than normal. This increases the baby’s risks during pregnancy and delivery, and later. Things that can cause babies to be small for gestational age are listed below.

Problems with the mother

  • High blood pressure
  • Chronic kidney disease
  • Diabetes
  • Heart disease or respiratory disease
  • Malnutrition or anemia
  • Infection
  • Alcohol or drug use
  • Cigarette smoking
  • Weighing less than 100 pounds

Problems with the uterus and placenta

  • Decreased blood flow in the uterus and placenta
  • Placenta detaches from the uterus
  • Placenta attaches low in the uterus
  • Infection in the tissues around the baby

Problems with the developing baby

  • Multiple pregnancy, such as twins or triplets
  • Infection
  • Birth defects
  • Chromosome problems


Small for gestational age babies may look mature, but they are smaller than other babies of the same gestational age. They may be small all over, or they may be of normal length and size but have lower weight and body mass. These babies may be born:

  • Premature. Before 37 weeks of pregnancy.
  • Full-term. Between 37 and 38 weeks (early term) through 41 weeks.
  • Post-term. After 42 weeks of pregnancy.

Many small for gestational age babies have low birth weight. But not all are premature. They may not have the same problems as premature babies. Other babies, especially those with intrauterine growth restriction, may look thin and pale, and have loose, dry skin. The umbilical cord is often thin and dull-looking rather than shiny and fat.


Babies with this problem are often diagnosed with intrauterine growth restriction before birth. During pregnancy, a baby’s size can be guessed in different ways. The height of the top of a mother’s uterus can be measured from the pubic bone. This measurement in centimeters usually links with the number of weeks of pregnancy after the 20th week. If the measurement is low for the number of weeks, then the baby may be smaller than expected.

Other tests used for diagnosis may include:

  • Ultrasound to estimate the baby’s size
  • Doppler flow to help check blood flow to the baby during pregnancy
  • Mother’s weight gain to tell how a baby is growing during pregnancy
  • Baby’s birth weight as compared with the gestational age once the baby is born. The healthcare provider may use a formula to figure out the baby’s body mass.


Treatment will depend on your child’s symptoms, age, and general health. It will also depend on how severe the condition is.

Babies with this problem may be physically more mature than their small size would suggest. But they may be weak and less able to take large feedings or stay warm. Treatment may include:

  • Temperature-controlled beds or incubators
  • Tube feedings if the baby does not have a strong suck
  • Blood tests to check for low blood sugar
  • Watching oxygen levels

Babies who are also premature may have other needs. They may need oxygen and a breathing machine (ventilator).


Babies who are small for gestational age or who have intrauterine growth restriction may have problems at birth. These can include:

  • Lower oxygen levels than normal
  • Low Apgar scores
  • Breathing in the first stools (meconium) passed in the womb. This can cause breathing problems.
  • Low blood sugar
  • Difficulty keeping a normal body temperature
  • Too many red blood cells


Prenatal care is important in all pregnancies. It is especially helpful to see any problems with the baby’s growth. For a healthy pregnancy, stop smoking if you smoke, and don't use drugs or alcohol while you are pregnant. Eating a healthy diet during pregnancy may also help.

Key Points

  • Small for gestational age means a baby is smaller than expected for the number of weeks of pregnancy.
  • Although some babies are small because their parents are small, most babies who are small for gestational age have growth problems that happen during pregnancy.
  • When the unborn baby does not get enough oxygen or nutrients during pregnancy, he or she does not grow as much as normal.
  • The condition is often suspected before birth.
  • Prenatal care is important in all pregnancies. It is especially helpful to see any growth problems of the developing baby.

Next Steps

Tips to help you get the most from a visit to your child’s healthcare provider:

  • Know the reason for the visit and what you want to happen.
  • Before your visit, write down questions you want answered.
  • At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you for your child.
  • Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
  • Ask if your child’s condition can be treated in other ways.
  • Know why a test or procedure is recommended and what the results could mean.
  • Know what to expect if your child does not take the medicine or have the test or procedure.
  • If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your child’s provider after office hours. This is important if your child becomes ill and you have questions or need advice.