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Birth Weight
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Pregnancy Reproduction

Birth Weight

Birth weight is the first weight of a newborn; extremes—low birth weight (under 5 lb 8 oz) or high birth weight (over 8 lb 13 oz)—can signal immediate and long‑term health risks, many of which are linked to maternal health and can often be mitigated.

Overview

What is birth weight?

Birth weight is the first weight of your baby, taken just after being born. A low birth weight means that the baby is less than 5 pounds, 8 ounces. A high birth weight means that the baby is more than 8 pounds, 13 ounces.

Causes & Risk Factors

Low birth weight

A baby with a low birth weight can be born too small, too early (premature), or both. This can happen for many different reasons. They include:

  • Health problems in the pregnant parent
  • Taking certain medicines during pregnancy
  • Substance use during pregnancy
  • Infections during pregnancy
  • Being pregnant with multiple babies
  • Problems with the placenta, the organ that brings oxygen and nutrients to the baby
  • Having small parents
  • Genetic conditions in the baby
  • Birth defects

High birth weight

Causes of high birth weight can include:

  • Having big parents
  • Diabetes in the pregnant parent
  • Certain genetic conditions
  • Too much weight gain during pregnancy

Problems Associated with Birth Weight

Low birth weight complications

Babies with low birth weight may be more at risk of certain health problems. They include immediate problems, such as:

  • Breathing problems
  • Infections
  • Hypoglycemia (low blood sugar)
  • Jaundice
  • Trouble keeping warm

There is also a higher risk of longer‑term problems, including:

  • Delayed motor and social development
  • Learning disabilities
  • Certain health conditions as an adult, such as heart disease, high blood pressure, diabetes, and obesity

High birth weight complications

High birth weight can be a concern because it can make delivery of the baby difficult and raise the risk of birth injuries. The baby is at higher risk of problems with:

  • Blood sugar
  • Breathing problems
  • Jaundice

Prevention

Can birth weight problems be prevented?

You may be able to prevent some birth weight problems by:

  • Getting regular checkups during pregnancy
  • Getting the right amount of nutrition and calories during pregnancy
  • Controlling your blood sugar if you have diabetes
  • Avoiding substance use during pregnancy

Frequently Asked Questions

Ultrasound estimates fetal weight by measuring the baby's head circumference, biparietal diameter, abdominal circumference, and femur length. While useful for tracking growth trends, ultrasound estimates have an average margin of error of 10% to 15%, and accuracy tends to decrease in the late third trimester. Clinicians use these measurements alongside maternal fundal height and clinical risk factors to guide delivery planning.
Strict glycemic control significantly lowers the risk of fetal macrosomia (birth weight over 8 pounds, 13 ounces). For gestational or preexisting diabetes, target glucose levels are typically a fasting reading of 95 mg/dL or lower, a one-hour post-meal reading of 140 mg/dL or lower, and a two-hour post-meal reading of 120 mg/dL or lower, adjusted according to the obstetric team's guidelines.
Yes. Most healthy newborns lose between 5% and 10% of their birth weight within the first 3 to 5 days of life due to the loss of excess fluid and the small initial intake of colostrum. Pediatricians expect babies to regain their birth weight by 10 to 14 days of age. If weight loss exceeds 10%, an evaluation of infant feeding mechanics and milk supply is necessary.
Low-birth-weight infants have less insulating body fat and smaller energy reserves. Caregivers should practice skin-to-skin contact (kangaroo care) and adjust room temperatures to prevent hypothermia. Feedings must occur on a strict schedule, typically every 2 to 3 hours around the clock, to prevent hypoglycemia and ensure adequate caloric intake. Frequent hand hygiene and limiting exposure to crowds are critical to shield their immature immune systems from infection.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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