Health - Adverse Birth Outcomes
The period of pregnancy, also called gestation, plays an important role in an infant's chance of survival and health for years to come. Two key factors used to help understand the quality of a pregnancy are how long it lasted (length of gestation) and birth weight.
On this page:
- Indicators
- About the Adverse Birth Outcomes Indicators
- Data Sources and Methods - Adverse Birth Outcomes
- Related Links
Indicators
H12: Babies born preterm
Web update: 2025
Key Information
- In 2023, 1 in 10 babies were born preterm, before 37 weeks of gestation.
- In 2023, Black non-Hispanic women had the highest rate of preterm birth, compared with women of other races/ethnicities. About 1 in 7 infants born to Black non-Hispanic women were born prematurely in that year.
- The preterm birth rate varies depending on the age of the mother. In 2023, women ages 20 to 39 years had the lowest rate of preterm birth, compared with women under 20 years and women 40 years and older.
- Twins, triplets, and other multiple birth babies are 7 times more likely to be born preterm compared with singleton babies.
Data Characterization
Data from this indicator are obtained from a database maintained by the National Center for Health Statistics.
The database collects information from birth certificates for virtually all births in the United States.
Length of gestation is recorded on each birth certificate.
H13: Babies born at full term with low birth weight
Web update: 2025
Key Information
- In 2023, the rate of full-term low birth weight for women of all race/ethnicities was almost 3%, and has been increasing since 2007. Values prior to 2007 are not comparable due to a change in the measure for length of gestation.
- The rate of full-term low birth weight varies by race/ethnicity. In 2023, 5% of Black non-Hispanic women had low birth weight babies.
- The rate of low birth weight among babies born at full term varies by the age of the mother. In 2023, women ages 20 to 39 years had the lowest rate of full-term low birth weight infants, 2.7%. Women under 20 years had the highest rate of full-term low birth weight infants at 4.3%.
- Twins, triplets, and other multiple birth babies born at full term are more than 3 times as likely to have low birth weight compared with singleton babies.
Data Characterization
Data from this indicator are obtained from a database maintained by the National Center for Health Statistics.
The database collects information from birth certificates for virtually all births in the United States.
Birth weight and length of gestation are recorded on each birth certificate.
About the Adverse Birth Outcomes Indicators
Two measures that may be used to understand the quality of an infant's gestation are length of gestation (pregnancy length) and birth weight. Preterm birth is defined as before 37 completed weeks of gestation. Low birth weight infants are defined as weighing less than 2,500 grams (about 5 pounds, 8 ounces) at full term. Preterm and low birth weight infants are at greater risk for mortality and a variety of health and developmental problems, both in childhood and adulthood.
A growing number of studies have examined the possible role that exposure to environmental contaminants may play in the causation of preterm birth and low birth weight. The Surgeon General has determined that exposure of pregnant women to environmental tobacco smoke (ETS) reduces birth weight and the evidence suggests a potential relationship with preterm birth. The Surgeon General has stated that there is no risk-free level of exposure to ETS. Additionally, the National Toxicology Program has concluded that maternal exposure to lead is known to cause reduced fetal growth, and that there is limited evidence of an association with preterm birth. Finally, some studies have reported associations between air pollution or other environmental contaminants and adverse birth outcomes.
For historical and contextual information about adverse birth outcomes and these indicators, see the Adverse Birth Outcomes section of America's Children and the Environment, Third Edition (pdf) .
Data Sources and Methods - Adverse Birth Outcomes
The National Center for Health Statistics, a division of the Centers for Disease Control and Prevention (CDC), maintains the National Vital Statistics System (NVSS) which compiles national data on gestational ages and birth weights from birth certificate registration data from states and other U.S. jurisdictions. The NVSS data are provided through contracts between the CDC and vital registration systems operated in each state, which are legally responsible for the registration of vital events including births, deaths, marriages, divorces, and fetal deaths. Birth certificates provide information on characteristics of both the infant and parents, including the weight of the infant and the length of gestation. Length of gestation is recorded in completed weeks and is based on clinical estimation, usually from the date of the woman's last menstrual period or ultrasound.
Indicator H12 uses the NVSS data to present the percentage of babies born preterm (defined as a period of gestation less than 37 completed weeks) stratified by race/ethnicity. Indicator H13 uses the data to present the percentage of babies that are both born at term (defined as a period of gestation of at least 37 completed weeks) and have low birth weight (defined as a weight less than 2,500 grams), stratified by race/ethnicity.
- Detailed Methods for Indicators H12 and H13 (pdf)
- Metadata for National Health Interview Survey (NHIS)
Related Links
- U.S. EPA Integrated Science Assessment: Particulate Matter (PM)
- Centers for Disease Control and Prevention (CDC): Maternal and Child Health
- Institute of Medicine (IOM): Preterm Birth: Causes, Consequences, and Prevention
- National Toxicology Program (NTP): Health Effects of Low-Level Lead Evaluation
- U.S. Department of Health & Human Services (HHS): The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General