What does it mean to be small for gestational age?

Small for gestational age is a term used to describe babies who are smaller than expected for the number of weeks of pregnancy. These babies have a birth weight below the 10th percentile. This means they are smaller than 90% of (most) other babies of the same gestational age. Most babies 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.

What causes babies to be small for gestational age?

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 fetal growth restriction (FGR). This happens when the unborn baby has trouble getting 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) can happen because of chromosome problems in the baby. It can also happen 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's often linked to other problems.

Who is at risk for being small for gestational age?

When the unborn baby has trouble getting 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 usual (or expected) 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.

What are the symptoms of small for gestational age babies?

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.

How are small for gestational age babies diagnosed?

Babies with this problem are often diagnosed with FGR 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 often 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.

How are small for gestational age babies treated?

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 doesn't have a strong suck

• Blood tests to check for low blood sugar

• Watching oxygen levels

Babies who are also premature may have other needs. For example, they may need intravenous nutrition, oxygen and/or a breathing machine (ventilator).

What are possible complications of being small for gestational age?

Babies who are small for gestational age or who have FGR 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

• Trouble keeping a normal body temperature

• Too many red blood cells

• Problems with electrolytes (refeeding syndrome)

Can small size for gestational age be prevented?

Prenatal care is important in all pregnancies. It's 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 about small for gestational age babies

• Small for gestational age means a baby is smaller than expected for the number of weeks of pregnancy.

• 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.

• When the unborn baby has trouble getting oxygen or nutrients during pregnancy, they don't grow as much as expected.

• The condition is often suspected before birth.

• Prenatal care is important in all pregnancies. It's 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.