What is low birth weight?

Low birth weight is the birth of a child weighing less than 2.5 kg. Some babies with low birth weight are healthy even when they are small. But low birth weight can lead to serious health problems in some babies. A very young baby may have difficulty eating, gaining weight, and fighting infections at birth. Some may also have long-term health problems.

Why does the baby have a low birth weight?

There are two main reasons:

Premature delivery.
Intrauterine growth restriction. This means that the baby is not gaining the weight it should have been before birth. Some babies may have low birth weight simply because their parents are small. Others may have a low birth weight because something slowed or stopped their growth during pregnancy. Your doctor measures your belly and uses ultrasound to track your baby's growth during pregnancy.

If your doctor thinks your child's growth is limited, you may have more frequent ultrasounds (every 2 to 4 weeks) to monitor your child's growth. Your doctor may also perform other tests, such as heart rate monitoring and tests for infections or birth defects. Babies with birth defects are more likely to be born prematurely.

Are you at risk of having a low birth weight baby?

Some things may make you more likely than others to have a low birth weight baby. These are the so-called risk factors. Having a risk factor does not mean that you will definitely have a low birth weight baby, but it can increase your chances. Talk to your doctor about what you can do to reduce your risk.

Medical risk factors for having a baby with a low birth weight

Preterm labor. These are labors that start too early, before 37 weeks of gestation.
Chronic health problems. These are health problems that last a long time or recur over a long period of time. Chronic health problems should be treated by a doctor. Chronic conditions that can lead to a low birth weight baby include high blood pressure, diabetes, heart, lung and kidney problems.
Taking certain medicines to treat health problems such as high blood pressure, epilepsy, and blood clots. Tell your doctor about any prescription medicines you are taking. You may need to stop taking the drug or switch to a safer drug during pregnancy.
Infections. Some infections, especially infections of the internal reproductive organs during pregnancy, can slow down the growth of the baby in the womb. These include cytomegalovirus, rubella, chickenpox, toxoplasmosis, and some sexually transmitted infections.
Problems with the placenta. The placenta develops in the uterus and supplies the baby with food and oxygen through the umbilical cord. Certain problems with the placenta can reduce the supply of oxygen and nutrients to the baby, which can limit growth.
Insufficient weight gain during pregnancy. Pregnant women who do not gain enough weight during pregnancy are more likely to have a low birth weight baby than those who gain the correct weight. If you have an eating disorder or have been treated for an eating disorder, talk to your doctor. Your doctor may monitor you and your baby closely throughout your pregnancy to prevent complications and make sure you are both healthy.
Having a child who was born too early or had a low birth weight in the past.
Multiple pregnancy (twins, triplets and more). More than half of multiple children have low birth weight.
Smoking, alcohol use, illegal drug use and prescription drug abuse. Pregnant women who smoke are 3 times more likely to have an underweight baby than non-smokers. Smoking, drinking alcohol, using street drugs, and misusing prescription drugs during pregnancy can slow the growth of the baby in the womb and increase the risk of preterm birth and birth defects.
Exposure to air pollution or lead
Being a member of a group that is experiencing the effects of racism and health inequalities.
Domestic violence. This is when your partner hurts you or insults you. This includes physical, sexual and emotional abuse.
Age. As a teenager (especially younger than 15) or older than 35, you are more likely than other parents to have a baby with a low birth weight.

Does low birth weight cause problems for the baby?

Yes. Babies who weigh less than they should at birth are more likely than normal weight babies to have health problems. Some require special care in a hospital's neonatal intensive care unit to treat medical problems. These include:

Breathing problems such as respiratory distress syndrome. Children with respiratory distress syndrome lack a protein called surfactant, which keeps the small air sacs in the child's lungs from collapsing. Surfactant treatment helps these children breathe easier. Infants with respiratory distress syndrome may also need oxygen and other breathing aids to keep their lungs working.
Hemorrhage in the brain (intraventricular hemorrhage). Most cerebral hemorrhages are light and go away on their own. Heavier bleeding can put pressure on the brain, which can lead to fluid buildup in the brain. This can lead to brain damage. In some cases, the surgeon may insert a tube into the baby's brain to drain fluid.
Patent ductus arteriosus. A patent ductus arteriosus occurs when the opening between two large blood vessels leading away from the heart does not close properly. This can cause extra blood flow to the lungs. In many babies with a patent ductus arteriosus, the opening closes on its own a few days after birth. Some children require medicine or surgery to close the hole.
Necrotizing enterocolitis. The child has intestinal problems. The intestines are long tubes that are part of the digestive system. The digestive system helps the body break down food. Necrotizing enterocolitis can be dangerous for the baby and can lead to feeding problems, bloating, and other complications. Children with necrotizing enterocolitis are treated with antibiotics and fed intravenously. Some children require surgery to remove damaged parts of the intestine.
Retinopathy of prematurity. This eye disease occurs when a baby's retina does not fully develop within a few weeks of birth.
Jaundice. This is a condition in which the eyes and skin of a child turn yellow. It happens when there is too much of a substance called bilirubin in the blood.
Infections. The immune system protects the body from infections. In a baby born too early, the immune system may not be fully developed and unable to fight infection.

Does low birth weight cause problems later in life?

Babies born too small may be more likely than others to have certain health problems later in life, including:

Diabetes
Heart disease
High blood pressure
Intellectual and developmental disabilities
Metabolic syndrome
Obesity

If you have a baby who weighs less than he should have at birth, talk to his doctor about what you can do to help your baby be healthy. As your child grows, make sure he eats healthy foods, stays active, and gets all his checkups. Regular checkups can help your child's doctor identify any health issues that may cause problems as your child grows. These check-ups also help ensure that your child gets all the vaccines they need to protect against certain harmful diseases.