Small for gestational age (SGA) is a term used to describe a baby who is smaller than the usual amount for the number of weeks of pregnancy. SGA babies usually have birthweights below the 10th percentile for babies of the same gestational age. This means that they are smaller than 90 percent of all other babies of the same gestational age.
SGA babies may appear physically and neurologically mature but are smaller than other babies of the same gestational age. SGA babies may be proportionately small (equally small all over) or they may be of normal length and size but have lower weight and body mass. SGA babies may be premature (born before 37 weeks of pregnancy), full term (37 to 41 weeks), or post term (after 42 weeks of pregnancy).
Although some babies are small because of genetics (their parents are small), most SGA babies are small because of fetal growth problems that occur during pregnancy. Many babies with SGA have a condition called intrauterine growth restriction (IUGR). IUGR occurs when the fetus does not receive the necessary nutrients and oxygen needed for proper growth and development of organs and tissues. IUGR can begin at any time in pregnancy. Early-onset IUGR is often due to chromosomal abnormalities, maternal disease, or severe problems with the placenta. Late-onset growth restriction (after 32 weeks) is usually related to other problems.
Some factors that may contribute to SGA and/or IUGR include the following:
When the fetus does not receive enough oxygen or nutrients during pregnancy, overall body and organs growth is limited, and tissue and organ cells may not grow as large or as numerous. Some of the conditions that cause SGA and IUGR restrict blood flow through the placenta. This can cause the fetus to receive less oxygen than normal, increasing the risks for the baby during pregnancy, delivery, and afterwards.
Babies with SGA and/or IUGR may have problems at birth including the following:
The baby with SGA is often identified before birth. During pregnancy, a baby's size can be estimated in different ways. The height of the fundus (the top of a mother's uterus) can be measured from the pubic bone. This measurement in centimeters usually corresponds with the number of weeks of pregnancy after the 20th week. If the measurement is low for the number of weeks, the baby may be smaller than expected.
Although many SGA babies have low birthweight, they are not all premature and may not experience the problems of premature babies. Other SGA babies, especially those with IUGR, appear thin, pale, and with loose, dry skin. The umbilical cord is often thin, and dull-looking rather than shiny and fat. They sometimes have a wide-eyed look.
Other diagnostic procedures may include the following:
Specific treatment for SGA will be determined by your baby's physician based on:
Babies with SGA may be physically more mature than their small size indicates. But they may be weak and less able to tolerate large feedings or to stay warm. Treatment of the SGA baby may include:
Babies who are SGA and are also premature may have additional needs including oxygen and mechanical help to breathe.
Prenatal care is important in all pregnancies, and especially to identify problems with fetal growth. Stopping smoking and use of substances such as drugs and alcohol are essential to a healthy pregnancy. Eating a healthy diet in pregnancy may also help.