Low Birth Weight

A Physical health measure
Loading interactive model…

About

Percentage of live births with low birth weight (< 2,500 grams). The 2025 Annual Data Release used data from 2017-2023 for this measure.

For most states and counties, updated data were released on using data from 2018-2024.

Low birth weight can be due to preterm births (<37 weeks of gestation) and intrauterine growth restrictions that are associated with increased infant morbidity and mortality risks.1 Structural barriers to proper nutrition and adequate prenatal care can result in slowed intrauterine growth.2,3 Maternal stress and living in a neighborhood with a high level of pollution are associated with lower birth weight4 as well as substance misuse during pregnancy.5 Other factors that increase the likelihood of preterm births include multiple births, pre-eclampsia, and infections such as chorioamnionitis, bacterial vaginosis, and sepsis.2,3

Low birth weight is an important public health indicator that can be used to assess maternal health, nutrition, healthcare delivery, and poverty.1-3 Infants born with low birth weight have approximately 20 times greater chance of dying than those with normal birth weight.3 Infants who survive may face adverse health outcomes such as decreased growth, lower IQ, impaired language development, and chronic conditions (e.g., obesity, diabetes, cardiovascular disease) during adulthood.3,6

Loading interactive model…

Data and methods

Data Source

National Center for Health Statistics - Natality Files

The National Center for Health Statistics (NCHS) provides birth data drawn from the National Vital Statistics System (NVSS). Data are submitted to the NVSS by the vital registration systems operated in the jurisdictions legally responsible for registering vital events (i.e., births, deaths, marriages, divorces, and fetal deaths). These data are sourced from the NCHS Births (Natality) - All counties (2017-2024) file, as compiled from data provided by the 57 vital statistics juridictions through the Vital Statistics Cooperative Program. Data for the Connecticut Planning Regions are provided by the State Vital Records Office at the Connecticut Department of Public Health.

Website to download data

Key Measure Methods

Low Birth Weight is a percentage

Low Birth Weight is the percentage of live births where the infant weighed less than 2,500 grams (approximately 5 lbs., 8 oz.).

Births are counted in the mother's county of residence

Births are counted in the county corresponding to the mother’s address on the child’s birth certificate, regardless of where the child was born.

Some data are suppressed

A missing value is reported for counties with fewer than 10 low birth weight births in the time frame.

Caution should be used when comparing these estimates across years

Updates to race categories in the 2024 Annual Data Release mean that comparisons with previous years should be made with caution.

Numerator

The numerator is the number of live births for which the infant weighed less than 2,500 grams (approximately 5 lbs., 8 oz.) over seven years.

Denominator

The denominator is the total number of live births for which weight was recorded over seven years.

Can This Measure Be Used to Track Progress

This measure can be used to track progress with some caveats. It is important to note that the estimate provided in the Health Snapshots is a seven-year average. However, in most counties, it is relatively simple to obtain single-year estimates from the resource below.

Finding More Data

Disaggregation means breaking data down into smaller, meaningful subgroups. Disaggregated data are often broken down by characteristics of people or where they live. Disaggregated data can reveal inequalities that are otherwise hidden. These data can be disaggregated by:

  • Age
  • Gender
  • Race
  • Education

We recommend starting with the CDC WONDER database, which contains information on birth rates by race, ethnicity, age, and more for counties with populations of 100,000 or more. Please note that demographic information is available for mother (age, race, education, income, subcounty area) and infant (sex, race).

References

  1. Hughes MM, Black RE, Katz J. 2500-g Low birth weight cutoff: History and implications for future research and policy. Maternal and Child Health Journal. 2017;21:283-289.
  2. Osterman MJK, Hamilton BE, Martin JA, Driscoll AK, Valenzuela CP. Births: Final data for 2021. National Vital Statistics Reports. 2023;72(1). https://www.cdc.gov/nchs/data/nvsr/nvsr72/nvsr72-01.pdfhttps://www.cdc.gov/nchs/data/nvsr/nvsr70/nvsr70-17.pdf
  3. Cutland CL, Lackritz EM, Mallett-Moore T, et al. Low birth weight: Case definition & guidelines for data collection, analysis, and presentation of maternal immunization safety data. Vaccine. 2017;35(48 Pt A):6492-6500.
  4. Niu Z, Habre R, Chavez TA, et al. Association between ambient air pollution and birth weight by maternal individual- and neighborhood-level stressors. JAMA Network Open. 2022;5(10):e2238174.
  5. Forray A. Substance use during pregnancy [version 1; peer review: 2 approved]. F1000Research. 2016;5(F1000 Faculty Rev):887.
  6. UNICEF. Low birthweight. 2023. Accessed February 7, 2023. https://data.unicef.org/topic/nutrition/low-birthweight/