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 drug use 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
- 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)
- Article: Maternal Serum Albumin Redox State Is Associated with Infant Birth Weight...
- Article: Lower birth weight-for-age and length-for-age z-scores in infants with in-utero HIV...
- Article: Maternal Obesity and Risk of Low Birth Weight, Fetal Growth Restriction,...
- Birth Weight -- see more articles
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