mom kissing her baby's feet

What Is Low Birth Weight?

By Kerry Weiss
Reviewed by Alyssa Quimby, M.D.
January 18, 2023

Newborn weights vary. Most full-term babies weigh between 5 pounds, 8 ounces and 8 pounds, 13 ounces. But some babies are smaller than that. It’s important to know what low birth weight means and what you can do about it.

What Is Low Birth Weight?

Low birth weight is when a baby weighs less than 5 pounds, 8 ounces at birth. About 1 in 12 babies in the U.S. are born with a low birth weight.

Is Low Birth Weight a Problem?

Some babies with low birth weight are healthy. Others can have health problems at birth and later in life. “The lower the birth weight, the greater the risk,” says Soniya Mehra, M.D. Mehra is a pediatrician at Bayside Medical group at Stanford Medicine Children’s Health in Fremont, California.

Babies with low birth weight may have a hard time:

  • Breathing
  • Eating
  • Gaining weight
  • Staying warm
  • Fighting illness

Babies with low birth weight can also have a higher risk of:

  • Brain issues
  • Stomach problems
  • Eye problems
  • Jaundice (yellow skin and eyes)
  • Sudden infant death syndrome (SIDS)

Having a low birth weight may also increase risk of issues later in life, such as:

  • Diabetes
  • Heart disease
  • High blood pressure
  • Metabolic syndrome
  • Obesity
  • Problems learning or developing

What Causes Low Birth Weight?

Low birth weight is most often caused by preterm birth, Mehra says.

The second-most common cause is when a baby does not gain enough weight before it is born. This could be because a parent is small. Or it could be due to issues with the pregnant parent’s or baby’s health. It could also be a sign the placenta is not working right.

How Can I Reduce the Risk of Low Birth Weight?

The best thing you can do is take care of your health. And that goes for before and while you are pregnant, says Ellie Ragsdale, M.D. Ragsdale is an ob-gyn at University Hospitals in Cleveland.

Some health issues during pregnancy come with a higher risk of having a baby with a low birth weight, Ragsdale explains. This includes:

  • High blood pressure
  • Heart disease
  • Obesity

Healthy lifestyle habits can help lower your baby’s risk of low birth weight, Ragsdale says. Here’s what you can do:

  • Manage any health issues you have.
  • Don’t smoke, drink alcohol, or use drugs.
  • Do your best to eat a healthy diet.
  • Aim for healthy weight gain while pregnant.
  • Go to all your doctor visits to monitor your health and your baby’s health.

What Happens If My Baby Has Low Birth Weight?

Not all babies with low birth weight can go home right away. They may need to spend time being cared for in a special hospital unit called the NICU. “NICU” stands for “neonatal intensive care unit.”

Once your baby comes home, it’s important to go to every scheduled doctor visit, Mehra says. That way your baby’s doctor can closely watch their growth and health. They will also keep your baby up to date with vaccines to protect their health.

Many babies with low birth weight can be healthy. Most “catch up” in growth when there are no other problems.

You May Also Like: