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.
What can cause 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
What problems can low birth weight cause?
Babies with low birth weight may be more at risk of certain health problems. They include immediate problems, such as:
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
What can cause 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
What problems can high birth weight cause?
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
Can birth weight problems be prevented?
You may be able to prevent some birth weight problems by:
Statistics and Research
- FastStats: Birthweight and Gestation (National Center for Health Statistics)
- ClinicalTrials.gov: Infant, Low Birth Weight (National Institutes of Health)
- ClinicalTrials.gov: Infant, Small for Gestational Age (National Institutes of Health)
- ClinicalTrials.gov: Large for Gestational Age (National Institutes of Health)
Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)
Find an Expert
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Also in Spanish
- KidsHealth (Nemours Foundation)
- March of Dimes Birth Defects Foundation Also in Spanish