Small for gestational age

What causes small for gestational age (SGA)?

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 doesn't 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:

Maternal factors:

• high blood pressure
• chronic kidney disease
• advanced diabetes
• heart or respiratory disease
• malnutrition, anemia
• infection
• substance use (alcohol, drugs)
• cigarette smoking

Factors involving the uterus and placenta:

• decreased blood flow in the uterus and placenta
• placental abruption (placenta detaches from the uterus)
• placenta previa (placenta attaches low in the uterus)
• infection in the tissues around the fetus

Factors related to the developing baby (fetus):

• multiple gestation (twins, triplets, etc.)
• infection
• birth defects
• chromosomal abnormality

Why is small for gestational age (SGA) a concern?

When the fetus doesn't receive enough oxygen or nutrients during pregnancy, the fetus's 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 your baby during pregnancy, delivery and after he is born.

Babies with SGA and/or IUGR may have problems at birth, including:

• decreased oxygen levels
• low Apgar scores (an assessment that helps identify babies with difficulty adapting after delivery)
• meconium aspiration (inhalation of the first stools passed in utero) which can lead to difficulty breathing
• hypoglycemia (low blood sugar)
• difficulty maintaining normal body temperature
• polycythemia (too many red blood cells)