Birth weight is the first weight of your baby, taken just after he or she is born. A low birth weight is less than 5.5 pounds. A high birth weight is more than 8.8 pounds.
A low birth weight baby can be born too small, too early (premature), or both. This can happen for many different reasons. They include health problems in the mother, genetic factors, problems with the placenta and substance abuse by the mother.
Some low birth weight babies may be more at risk for certain health problems. Some may become sick in the first days of life or develop infections. Others may suffer from longer-term problems such as delayed motor and social development or learning disabilities.
High birth weight babies are often big because the parents are big, or the mother has diabetes during pregnancy. These babies may be at a higher risk of birth injuries and problems with blood sugar.
Centers for Disease Control and Prevention
Statistics and Research
- Child Health USA 2014: Preterm Birth and Low Birth Weight (Health Resources and Services Administration)
- FastStats: Birthweight and Gestation (National Center for Health Statistics)
- Gestational Age, Infant Birth Weight, and Subsequent Risk of Type 2 Diabetes in Mothers: Nurses' Health Study II (Centers for Disease Control and Prevention) Also in Spanish
- Iron Supplements Reduce Behavior Problems in Low Birth Weight Infants (American Academy of Pediatrics)
- ClinicalTrials.gov: Birth Weight (National Institutes of Health)
- ClinicalTrials.gov: Fetal Macrosomia (National Institutes of Health)
- ClinicalTrials.gov: Gestational Age (National Institutes of Health)
- 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 ArticlesReferences and abstracts from MEDLINE/PubMed (National Library of Medicine)
Find an Expert
- KidsHealth (Nemours Foundation)
- March of Dimes Birth Defects Foundation Also in Spanish
- National Institute of Child Health and Human Development Also in Spanish