Small for Gestational Age (SGA)
A baby who is smaller than average during pregnancy is called small for gestational age (SGA). Gestational age is measured beginning on the first day of the last menstrual period before pregnancy. An SGA baby will often have a birth weight below 9 out of 10 babies of the same age. An SGA baby may be equally small all over. Or the baby may be a normal length and size but have a lower weight and body mass. The baby’s brain and organs are usually fully mature, but small. After birth, SGA babies may have certain problems with breathing and feeding. This means they may need more care.
Causes of SGA
Some babies are small because their parents are small. But most SGA babies are small because of growth problems that happen during pregnancy. One of these problems is intrauterine growth restriction (IUGR). IUGR happens when the baby doesn't get enough nutrients and oxygen for proper growth. IUGR can start at any time in pregnancy. Early IUGR is often caused by problems with chromosomes, a maternal health issue, or severe problems with the placenta. Late IUGR (after 32 weeks) is often caused by other problems, such as chronic hypertension or preeclampsia. In late IUGR, the growth in the baby's head circumference is not affected. But the baby's length and weight are affected.
Certain things may make SGA and IUGR more likely. These include maternal health issues, such as:
Other lifestyle choices and health history can make SGA and IUGR more likely. These include:
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Alcohol or drug use.
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Smoking.
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Conception using assisted reproductive technology.
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Exposure to certain medicines like blood thinners or seizure medicines.
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Advanced maternal age.
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Low weight before becoming pregnant.
They also include health issues with the baby or the uterus, such as:
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Infection.
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Birth defects.
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Chromosome problems.
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Less blood flow in the uterus and placenta.
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A placenta that detaches from the uterus (placental abruption).
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A placenta that grows too low in the uterus (placenta previa).
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Umbilical cord problems.
Being pregnant with twins, triplets, or other multiples can also make IUGR and SGA more likely.
Why does SGA matter?
SGA may show that the baby is getting less oxygen and nutrients than normal. This increases the health risks for the baby during pregnancy, delivery, and afterward. Babies with SGA may have problems at birth, such as:
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Lower oxygen levels.
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Low Apgar scores. This is an assessment that shows how a baby is doing right after delivery.
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Inhaling the first stools that are passed in utero (meconium aspiration). This can cause breathing problems.
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Low blood sugar (hypoglycemia).
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Trouble keeping normal body temperature.
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Too many red blood cells (polycythemia).
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Poor immune function.
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Low blood calcium.
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Feeding problems.
Diagnosing SGA
During pregnancy, a baby’s size can be estimated in different ways. The height of the top of the uterus (fundus) can be measured from the pubic bone. This height in centimeters often matches the number of weeks of pregnancy after the 20th week. If the number is lower than the number of weeks, the baby may be smaller than average.
Other tools for diagnosing SGA include:
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Ultrasound. This test uses sound waves and a computer to create pictures of the inside of the body. This is a more accurate way to estimate the size of a baby before birth. Measurements can be taken of the baby’s head and abdomen. The numbers are then compared with a growth chart.
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Uterine artery Doppler velocimetry (UADV). This test uses sound waves to measure blood flow. It can be done to look at blood flow through blood vessels in the baby’s brain and the umbilical cord.
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Cardiotocography. This test records the baby's heartbeat and uterine contractions. It is done when repeated ultrasound scans and UADV show problems that don't go away.
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Weight gain. Your weight gain during pregnancy can also help indicate your baby’s size. Small weight gain may mean a smaller baby.
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Gestational assessment. Babies are weighed in the first few hours after birth. The birth weight is compared with the expected weight for the baby’s gestational age.
After delivery, SGA babies may have other signs, such as:
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A body that looks thin and pale.
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Less skeletal muscles, less subcutaneous fat tissues (fat under the skin), and skin that is loose and dry.
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An umbilical cord that is thin and dull-looking instead of shiny and fat.
Treatment of SGA
The treatment of SGA is supportive care. A baby with SGA may be weak and less able to feed as well, or to stay warm. They may be put in a temperature-controlled bed or incubator to keep warm. Tube feedings may be done to make sure the baby has enough nutrition. Breastfeeding only from birth to 6 months of age is highly recommended.
Blood tests may be done to check blood sugar levels. And blood oxygen levels will be watched. If needed, extra oxygen or mechanical ventilation may be used to help the baby breathe. Serum and urine testing might be done to check for congenital infections. These are infections passed to a baby any time during pregnancy or during labor or delivery. Examples are toxoplasmosis and Cytomegalovirus. If the doctor thinks there might be other health issues present at birth, genetic testing might also be done.
Preventing SGA
Prenatal care is important in pregnancy. Regular visits to your doctor can help spot problems, such as SGA and IUGR. It's important to control any long-term (chronic) health conditions throughout your pregnancy. Discuss with your doctor the risks and benefits if you have been prescribed any medicines. Not using tobacco, alcohol, and other drugs is also important for a healthy pregnancy. Understand the importance of staying away from tobacco, alcohol, and drugs. Talk with your doctor if you need help to stop using tobacco, alcohol, or drugs.