Low birth weight means your baby was born weighing fewer than 5 pounds, 8 ounces (2,500 grams). The main causes of low birth weight include preterm birth and a condition called fetal growth restriction. Low weight at birth can lead to a number of complications. If your baby is born with low birth weight, they’ll likely need immediate treatment.

What Is Considered Low Birth Weight?

Low birth weight means your baby was born weighing fewer than 5 pounds, 8 ounces (2,500 grams). Birth weight is how much your baby weighs right after they’re born. Having a low weight at birth doesn’t mean your child will be below average in weight when they grow up. Some infants with low birth weight are healthy even though they’re small.

Your baby’s birth weight can help their providers figure out if your baby needs extra attention immediately after birth. For some babies, having a low birth weight can cause serious health issues. If your baby is very small at birth, they may have issues:

Some babies may have long-term health problems, too. If your baby has low weight at birth, a neonatologist and other providers will do everything they can to take care of your baby.

Symptoms and Causes

Symptoms of low birth weight

Infants born with low birth weight look much smaller than babies born at an average birth weight. Babies born full term (37 to 41 weeks of pregnancy) weigh between 5 pounds, 11.5 ounces (2,600 grams) and 8 pounds, 5.75 ounces (3,800 grams).

Your baby’s head may look bigger than the rest of their body. And they may appear thin with little body fat.

What causes low birth weight?

There are two main causes of low birth weight in infants: preterm birth and intrauterine growth restriction. One or both of these pregnancy complications may lead to your baby’s condition.

Preterm birth

Preterm birth, or premature birth, means your baby was born before 37 weeks of pregnancy. If your baby was born early, it means they spent less time growing and gaining weight in your uterus. A fetus gains a lot of its weight during the last few weeks of pregnancy.

Intrauterine growth restriction

Intrauterine growth restriction (IUGR) means your baby didn’t grow and gain the weight they should have before birth. Some infants have low birth weight because their biological parents are small. But for others, IUGR can occur because something slowed down or stopped their growth during pregnancy. This can occur due to issues with:

  • The placenta
  • Your health
  • The fetus’s health

Risk factors

Factors that may increase your risk of having a baby with low birth weight include:

  • Chronic illness during your pregnancy
  • Having an infection during your pregnancy
  • Taking certain medications during your pregnancy
  • Using substances like alcohol or tobacco during your pregnancy
  • Not gaining or maintaining enough weight during your pregnancy
  • Being pregnant with multiples
  • Exposure to lead or unhealthy air
  • Preterm labor
  • Being 17 or younger or 35 or older
  • Nonmedical factors, like where you live and if you have access to good healthcare

Can low birth weight affect a baby?

Newborns with low birth weight are at a higher risk of certain health issues. Their tiny bodies aren’t as strong as babies born of typical birth weight. They may have trouble eating, gaining weight and fighting off infections.

Babies with low birth weight frequently have trouble staying warm because they have so little body fat. The lower your baby’s birth weight, the higher their risk for complications. These may include immediate problems, including:

What are the long-term effects of low birth weight?

Babies with low birth weight have a higher risk of developing long-term issues, like:

  • Developmental delays
  • Intellectual disability
  • Learning differences

They may also experience certain physical health conditions when they grow up, including:

  • High blood pressure
  • Heart disease
  • Diabetes
  • Obesity
  • Metabolic syndrome

Diagnosis and Tests

How doctors diagnose low birth weight

At your prenatal exams, your pregnancy care provider will estimate the size of your baby in different ways. One way they keep track is by simply monitoring your weight gain. Another way they measure is by tracking fundal height. Fundal height is the distance from the top of your uterus to your pubic bone. Your provider may also use ultrasound to keep an eye on the fetus’s growth and development.

After birth, a healthcare provider will weigh your baby within the first couple of hours. They’ll compare your baby’s weight with their gestational age (how far along you were in pregnancy) and record it in their medical record. The standard low birth weight definitions are:

  • Low birth weight: Fewer than 5 pounds, 8 ounces (2,500 grams)
  • Very low birth weight: Fewer than 3 pounds, 5 ounces (1,500 grams)
  • Extremely low birth weight: Fewer than 2 pounds, 3 ounces (1,000 grams)

Management and Treatment

How is low birth weight treated?

Your baby’s healthcare provider will figure out what treatment your baby needs. They’ll base treatment on your baby’s:

  • Gestational age
  • Overall health
  • Medical history
  • Tolerance for medications, procedures or therapies

Treatment for low birth weight typically includes:

  • Care in the hospital’s neonatal intensive care unit (NICU)
  • Use of a temperature-controlled bed
  • Special feedings, sometimes through an intravenous (IV) line or with a tube into their stomach
  • Other treatments for complications

Babies with low weight at birth usually catch up in physical growth as long as there aren’t any other complications. Depending on your baby’s condition, their pediatrician may refer them to a specialist for follow-up care.

How do I take care of my baby when we leave the hospital?

If your baby was born with low birth weight, ask their healthcare provider what you should do to help them gain weight. As your child gets older, make sure they’re eating healthy foods and staying active. It’s also important that they get to all of their well-child check-ups.

At routine well-check appointments, your baby’s provider can look for health conditions that may cause issues as they get older. Your child can also get all of their necessary vaccinations at their well-child check-ups. Vaccines can help them stay protected from certain harmful diseases.

Outlook / Prognosis

What can I expect if my baby is born with low birth weight?

If your baby is born with low birth weight, they may need specialized care in the neonatal intensive care unit (NICU) of the hospital. They’ll stay in the NICU until they’ve gained enough weight. Your baby’s providers will let your baby leave the hospital when they’re well enough to go home.

What is the outlook (prognosis) for babies born with low birth weight?

Survival of newborns with low birth weight depends on how much they weigh at birth. Newborns weighing fewer than 1.1 pounds (500 grams) have the lowest survival rate. Talk to your baby’s healthcare provider to find out what you can expect in the months and years ahead.

Prevention

How to avoid low birth weight in infants

You may be able to prevent your baby from having a low weight at birth. During your pregnancy, make sure to:

  • Get regular check-ups.
  • Meet your provider’s recommended amounts of calories and nutrients.
  • Monitor your blood sugar (if you have diabetes).
  • Avoid using substances like alcohol and tobacco.

A note from Wockr

If your baby is born with low birth weight, you may experience a wide range of feelings. Make sure to lean on friends, family and loved ones for emotional support. It can be hard to see your tiny baby in the hospital NICU. But place your trust in your baby’s healthcare providers. They’re doing everything they can to help your baby gain weight and get ready to go home.