Low birth weight

What is low birth weight?

Very low birth weight is not always unhealthy or bad. For example, there is a tendency in some families to have small babies. A mother who is of small stature or has a small uterus could still have a perfectly healthy baby who weighs less than average.

During the first two years of growth, most catch up with other normal-weight children. 

Generally speaking, the lower the birth weight, the sicker the baby. These babies tend to be more prone to lung, heart and digestive problems and may be at a higher risk of developing medical conditions, such as diabetes and heart disease later in life. They also have issues with regulating body temperature.

Although not all babies born with low birth weight are unhealthy, it can cause complications both right after birth and later on in life, such as cerebral palsy (CP), blindness or deafness. 

Risk factors

• Smoking, alcohol or drug abuse are risk factors

• Exposures to lead from paint or pollution or mercury through eating oily fish are also related to low birth weight

• Having a low income, lack of education, age (being under 17 or over 35), and being black also can have an impact

• If you are having more than 1 baby, all may have low birth weights

• Certain genetic factors related to insulin resistance

• Previous maternal history of children born with very low birth weight

What are the different types of low birth weight?

There are various levels of low birth weight.

• Very low birth weight - birth weight is less than 3 lbs., 5 oz. (1500 grams)

• Extremely low birth weight - birth weight is less than 2 lbs., 3 oz. (1000 grams)

What are the signs and symptoms of low birth weight?

The final diagnosis of low birth weight will be made right after delivery. However, there are indicators that both the mother and her doctor can look at earlier in the pregnancy.

Few women will show symptoms. Trust your maternal instincts and don’t be afraid to bring this concern up during a visit with your doctor.

Since there are so few symptoms, your doctor will carefully measure your abdomen each time they see you. If the measurements don’t increase as they should, your doctor may suggest an ultrasound (US) test.

You may have some testing done that looks more for general health problems that could also affect your baby’s weight, for example, diabetes or nutritional disorders.

How is low birth weight diagnosed?

• Measurements - There are few tests for low birth weight before your baby is born. At each visit with your doctor, they should carefully measure your abdomen. If your baby doesn’t get bigger over time, an ultrasound (US) examination may be suggested.

• Ultrasound - The US bounces harmless sound waves off of your baby and any surrounding structures. It can tell more precisely the age of the baby and if there is anything restricting your baby’s growth inside the uterus. It can also show if you are carrying more than one baby, which

• Other tests may be performed as part of your regular visit. Most are looking for medical causes for low birth weight such as diabetes, infections, high blood pressure, or pre-eclampsia, all of which decrease blood flow to the baby.

• Nutrition - Most doctors will ask specific questions about how well, and what, you are eating. They will often ask specifically about milk and other sources of Vitamin D. Mom’s nutrition can have a big impact on how quickly your baby grows. Oily fish, such as sardines, herring, anchovies, salmon, trout, and mackerel should be eaten with caution because they contain mercury, which is related to a higher risk of low birth weight.

• Lead exposure - You should tell your doctor if you’ve been exposed to high levels of lead, which can cause low birth weight, so your doctor can test your blood for lead. Cigarette smoking also causes low birth weight.

• Amniotic fluid - Depending on the specific circumstances, your doctor may test the volume of amniotic fluid. This is the fluid that the baby floats in during pregnancy. Too much or too little can be an indicator that the placenta isn’t working properly. The placenta provides blood, oxygen and nutrition to your baby.

• After delivery - The diagnosis of low birth weight is made after delivery. If measurements of your baby show that weight and length are below the 10th percentile for age, your baby is considered low birth weight.

What are the causes of low birth weight?

• Premature birth (before 37 weeks of pregnancy or gestational age) is one of the major causes of low birth weight. The earlier a baby is born, the less it will generally weigh. Around 1 of every 8 babies born in the United States is premature and 7 of 10 low weight babies are premature.

• Fetal growth restriction - Another concern is fetal growth restriction. This means that a baby just did not gain the weight it should have before birth. For some, it is because something stopped or slowed their growth in the womb, such as an infection or problems with the placenta’s ability to provide food to the baby.

• Mom's health - For other babies, it may be related to the mom’s health such as high blood pressure, diabetes, or heart, lung and kidney disease. If the mother is undernourished or doesn’t gain enough weight, the chances are increased that the baby will also be underweight.

How is low birth weight treated?

During pregnancy

One of the best ways to treat low birth weight is to prevent it. Have regular checkups to make sure both you and your baby are healthy. These are also times to help you manage other health issues.

Eating properly “for two,'' getting adequate exercise and avoiding cigarettes, street drugs, alcohol and prescription medications, except under the guidance of your doctor, all work toward a healthy child.

Your doctor can treat low birth weight during pregnancy once problems are detected.

After the baby is born

At birth, your baby may need to spend extra time in the hospital so he or she can be closely watched. How long will depend on the birth weight, the reason for the low birth weight, any complications or other health problems, and how long it takes to reach an appropriate weight to go home.

Depending on the actual birth weight, your doctor may suggest extra feedings to help your baby gain weight and grow stronger. If your baby is very small, the best course may be to provide more nutritious or higher calorie supplements intravenously.

In many cases, an incubator will be used because low birth weight babies can have trouble regulating body temperature. Oxygen monitoring and blood tests are often used to follow progress.

• Neonatal Intensive Care Unit (NICU) - If your baby requires very close monitoring, he or she may be placed in the neonatal intensive care unit (NICU). These are set up specifically with the needs of premature or ill newborns in mind.

• Other medical concerns - Some low birth weight babies will have other medical concerns. These are treated on an individual basis as found. Even after a baby is born with low weight, successful treatment can improve your baby's current and future health.