Preterm Births: Last Menstrual Period (LMP) Estimates of Gestation
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- Definition: Percentage of infants born prior to 37 weeks of gestation, based on last menstrual period estimate of gestational age (e.g., in 2016, 8.7% of infants born to California women were born preterm).Number of infants born prior to 37 weeks of gestation, based on last menstrual period estimate of gestational age (e.g., in 2016, 41,863 infants born to California women were born preterm).
- Data Source: California Dept. of Public Health, Birth Statistical Master Files; CDC WONDER, Natality Public-Use Data (Feb. 2019).
- Footnote: County-level data reflect the mother's county of residence, not the county in which the birth occurred. Data exclude infants for whom dates of mothers' last menses were not reported. The notation S refers to data that have been suppressed because there were fewer than 20 preterm births. N/A means that data are not available.
Learn More About Low Birthweight and Preterm Births
- Measures of Low Birthweight and Preterm Births on Kidsdata.org
Kidsdata.org offers the following measures of low birthweight and preterm birth:
- The number and percentage of infants born at low birthweight (weighing less than 2,500 grams or approximately 5 lbs, 8 oz) overall, by mother's age, and by mother's race/ethnicity
- The number and percentage of infants born at very low birthweight (weighing less than 1,500 grams or approximately 3 lbs, 5 oz)
- The number and percentage of infants born preterm (before 37 weeks of gestation), calculated either by last menstrual period (LMP) or obstetric estimate (OE)
- Low Birthweight and Preterm Births
- Infant Mortality
- Prenatal Care
- Teen Births
- Why This Topic Is Important
Preterm birth and low birthweight are among the leading causes of infant death in the U.S., and they account for billions of dollars spent annually on health care and other services (1, 2, 3). Babies born prematurely (before 37 completed weeks of gestation) face increased risks of wide-ranging health complications and long-term disabilities, including but not limited to developmental delays, cerebral palsy, heart disease, and respiratory, vision, and hearing problems (4, 5). These risks drop significantly as gestational age increases. Health care professionals recommend waiting until 39 to 40 weeks of gestation for delivery, if possible, as critical infant growth and development occur in the final weeks of pregnancy (4, 5).
While many preterm babies are born too small, this is not always the case. For example, some infants are born prematurely but at a normal weight, and some are born full-term but at a low weight (1). Infants with a low birthweight (less than 5.5 lbs) have increased risks of numerous chronic health and developmental problems (2). Babies with a very low birthweight (less than 3.3 lbs) face even greater risks of adverse health outcomes (2).
Decades of research have shown large inequities in birth outcomes by race/ethnicity, even after controlling for income, with rates of preterm birth, low birthweight, and infant mortality consistently higher for the African American/black population than other groups (6). Many other factors also increase the risk of premature birth and low birthweight, such as low socioeconomic status, inadequate prenatal care, short intervals between pregnancies, maternal smoking or substance use issues, and women who: have had previous pregnancy complications; are carrying more than one baby; have certain uterine or cervical abnormalities; are age 40+ or under age 17; or have other health or mental health problems (2, 4, 7, 8, 9).Sources for this narrative:
1. Federal Interagency Forum on Child and Family Statistics. (2019). America's children: Key national indicators of well-being. Retrieved from: https://www.childstats.gov/americaschildren/health1.asp
2. Child Trends Databank. (2018). Low and very low birthweight infants. Retrieved from: https://www.childtrends.org/?indicators=low-and-very-low-birthweight-infants
3. March of Dimes. (2015). The impact of premature birth on society. Retrieved from: https://www.marchofdimes.org/mission/the-economic-and-societal-costs.aspx
4. Centers for Disease Control and Prevention. (2019). Preterm birth. Retrieved from: https://www.cdc.gov/reproductivehealth/maternalinfanthealth/pretermbirth.htm
5. Kardatzke, M. A., et al. (2017). Late preterm and early term birth: At-risk populations and targets for reducing such early births. NeoReviews, 18(5), e265-e276. Retrieved from: http://neoreviews.aappublications.org/content/18/5/e265
6. March of Dimes. (n.d.). Health equity and birth outcomes. Retrieved from: https://www.marchofdimes.org/materials/March-of-Dimes-Health-Equity-Birth-Outcomes-09192017.pdf
7. March of Dimes. (2018). Low birthweight. Retrieved from: https://www.marchofdimes.org/complications/low-birthweight.aspx
8. March of Dimes. (n.d.). Preterm labor and premature birth. Retrieved from: https://www.marchofdimes.org/complications/preterm-labor-and-premature-baby.aspx
9. Fuchs, F., et al. (2018). Effect of maternal age on the risk of preterm birth: A large cohort study. PLoS ONE, 13(1), e0191002. Retrieved from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0191002
- How Children Are Faring
The percentage of California infants born at low birthweight rose steadily from 6.1% in 1999 to 6.9% in 2005 and has remained fairly stable through 2016. Statewide, the number of infants born at very low birthweight was 5,445 in 2016 and accounted for 1.1% of all births, similar to percentages going back to 1995.
In 2016 and previous years, low birthweight varied across local areas and demographic groups. Among counties with data in 2016, percentages ranged from 5.2% to 7.9% for infants born at low birthweight and from 0.6% to 2% for infants born at very low birthweight. Statewide, women ages 45 and older consistently have the highest percentage of low birthweight babies (18.2% in 2016) when compared with younger mothers, as do African American/black women (11.6% in 2016) in comparison with other racial/ethnic groups.
Based on obstetric estimates (OE) estimates of gestational age, 8.6% of California infants were born preterm in 2016, down from 9.1% in 2008. Across counties with data, percentages of infants born preterm birth ranged from 6.2% to 10.6% in 2016.The U.S. Department of Health and Human Services has set Healthy People 2020 targets of 7.8% for infants born at low birthweight, 1.4% for infants born at very low birthweight, and 9.4% for infants born preterm. California has met these national objectives since at least 2008.
- Policy Implications
Reducing preterm births and low birthweight have been public health priorities for decades, as they are leading causes of infant mortality and major contributors to long-term disabilities (1). While California fares better than the nation as a whole on rates of babies born prematurely or at low weight, more work is needed, particularly in addressing inequities by race/ethnicity, income, and geography (2, 3, 8).
Some risk factors for low birthweight and preterm birth can be influenced by public and institutional policy focused on education, prevention, and treatment. Risk factors can be reduced through many different strategies, such as ensuring that women are in good health before pregnancy, avoid smoking and substance use while pregnant, and forgo elective deliveries before 39 weeks of gestation, along with broader strategies that address social determinants of health and systemic barriers to health care (4, 5, 6).
Policy and program options that could influence preterm births and low birthweight include:
For more policy ideas and research on this topic, see kidsdata.org’s Research & Links section, or visit the March of Dimes. Also see Policy Implications on kidsdata.org under Prenatal Care, Infant Mortality, and Teen Births topics.
- Supporting strategies to ensure that all women (and men) of reproductive age have access to continuous, affordable, comprehensive, culturally-sensitive health care before conception, during pregnancy, and after childbirth; as good health before conception can improve birth outcomes, ongoing health care provides an opportunity to identify and address key health risks before pregnancy, such as heart disease and unhealthy weight (1, 4, 5)
- As part of a comprehensive approach to women's health, integrating the following into routine care: reproductive planning and contraception counseling (including promotion of pregnancy intervals of at least 18 months), nutrition education, and screening and referrals for mental health, substance abuse, and social service needs (4, 6)
- Expanding access to timely, high-quality prenatal care, including group prenatal care, which can provide useful social support for pregnant women (4, 6)
- Continuing strategies to reduce smoking among pregnant women, and ensuring that effective tobacco cessation services are available and reimbursed by insurance (4, 6)
- Promoting efforts to reduce elective deliveries before 39 weeks of pregnancy, as important infant development occurs in the final weeks of gestation (4, 6)
- Reducing multiple births (twins, triplets, etc.) conceived with assisted reproductive technology (ART), as these births are more likely to be premature (6)
- Promoting use of evidence-based treatment to reduce specific risks of preterm birth, such as progesterone therapy for certain women and use of low-dose aspirin to prevent preeclampsia for women at risk (6, 7)
- Continuing research to further understand and address factors that contribute to preterm birth and low birthweight, including factors behind racial/ethnic disparities (4, 6, 8)
- Supporting effective strategies to increase public awareness about ways to promote healthy pregnancies; such efforts should be tailored to specific audiences and address topics such as reproductive planning, preconception health, folic acid supplementation, healthy weight, substance use, mental health, and other issues (4, 5, 6)
Sources for this narrative:
1. U.S. Department of Health and Human Services. (n.d.). Healthy People 2020: Maternal, infant, and child health. Retrieved from: https://www.healthypeople.gov/2020/topics-objectives/topic/maternal-infant-and-child-health
2. As cited on kidsdata.org, (i) Infants born at low birthweight; (ii) Preterm births: Obstetric estimates (OE) of gestation. (2019). California Department of Public Health & CDC WONDER.
3. California Department of Public Health, Maternal, Child and Adolescent Health Division. (2016). MIHA report, 2013-2014: Data from the Maternal and Infant Health Assessment (MIHA) Survey. Retrieved from: https://www.cdph.ca.gov/Programs/CFH/DMCAH/MIHA/CDPH%20Document%20Library/MIHA-AnnualReport-2013-2014-County-Regional.pdf
4. Secretary's Advisory Committee on Infant Mortality. (2013). Final recommendations for a national strategy to reduce infant mortality. U.S. Department of Health and Human Services. Retrieved from: https://www.hrsa.gov/advisory-committees/infant-mortality/reports.html
5. Verbiest, S., et al. (2016). Advancing preconception health in the United States: Strategies for change. Upsala Journal of Medical Sciences, 121(4), 222-226. Retrieved from: https://www.tandfonline.com/doi/full/10.1080/03009734.2016.1204395
6. March of Dimes. (2016). Prematurity campaign: 2015 progress report. Retrieved from: https://www.marchofdimes.org/glue/css-images/2015_prematurity_campaign_progress_report-1.pdf
7. Romero, R., et al. (2018). Vaginal progesterone for preventing preterm birth and adverse perinatal outcomes in singleton gestations with a short cervix: A meta-analysis of individual patient data. American Journal of Obstetrics and Gynecology, 218(2), 161-180. Retrieved from: https://www.ajog.org/article/S0002-9378(17)32343-8/fulltext
8. American College of Obstetricians and Gynecologists, Committee on Health Care for Underserved Women. (2015). Racial and ethnic disparities in obstetrics and gynecology. Obstetrics and Gynecology, 126, e130-134. Retrieved from: https://www.acog.org/Clinical-Guidance-and-Publications/Committee-Opinions/Committee-on-Health-Care-for-Underserved-Women/Racial-and-Ethnic-Disparities-in-Obstetrics-and-Gynecology
- Research & Links
- Websites with Related Information
- California Dept. of Public Health: Maternal, Child and Adolescent Health Division
- California Maternal Quality Care Collaborative
- California Perinatal Quality Care Collaborative
- California Preterm Birth Initiative. University of California San Francisco.
- Centers for Disease Control and Prevention: Before Pregnancy
- Centers for Disease Control and Prevention: Preterm Birth
- CityMatCH. University of Nebraska Medical Center.
- Health Resources and Services Administration: Maternal and Child Health Bureau
- March of Dimes: Premature Babies
- National Institute for Children's Health Quality
- Key Reports and Research
- Avoidance of Nonmedically Indicated Early-Term Deliveries and Associated Neonatal Morbidities. (2021). Obstetrics and Gynecology. American College of Obstetricians and Gynecologists.
- Birth Settings in America: Outcomes, Quality, Access, and Choice. (2020). National Academies Press. National Academies of Sciences, Engineering, and Medicine.
- California American Indian/Alaska Native Maternal and Infant Health Status Report. (2019). California Dept. of Public Health, Maternal, Child and Adolescent Health Division.
- Decomposition Analysis of Black-White Disparities in Birth Outcomes: The Relative Contribution of Air Pollution and Social Factors in California. (2017). Environmental Health Perspectives. Benmarhnia, T., et al.
- Fighting at Birth: Eradicating the Black-White Infant Mortality Gap. (2018). Samuel DuBois Cook Center on Social Equity & Insight Center for Community Economic Development. Smith, I. Z., et al.
- Infant Mortality in the United States, 2020: Data from the Period Linked Birth/Infant Death File. (2022). National Vital Statistics Reports. Ely, D. M., & Driscoll, A. K.
- Nurturing Care for Every Newborn: Thematic Brief. (2021). World Health Organization & The United Nations Children's Fund.
- Perinatal Equity Initiative. (2021). California Dept. of Public Health, Maternal, Child and Adolescent Health Division.
- Premature Babies. March of Dimes.
- Preterm Birth. (2023). World Health Organization.
- Preterm Birth and Social Support Services for Prenatal Depression and Social Determinants. (2021). PLOS ONE. Reno, R., et al.
- Quality of Care: Maternal Health and Childbirth. (2023). California Health Care Almanac. California Health Care Foundation. Joynt, J.
- Racial Disparities in Maternal and Infant Health: Current Status and Efforts to Address Them. (2022). Kaiser Family Foundation. Hill, L., et al.
- The Ethics of Perinatal Care for Black Women: Dismantling the Structural Racism in “Mother Blame” Narratives. (2019). Journal of Perinatal and Neonatal Nursing. Scott, K. A., et al.
- Worry About Racial Discrimination: A Missing Piece of the Puzzle of Black-White Disparities in Preterm Birth? (2017). PLOS ONE. Braveman P., et al.
- County/Regional Reports
- 2023 California County Scorecard of Children's Well-Being. Children Now.
- Air Pollution and Preterm Birth: A Time-Stratified Case-Crossover Study in the San Joaquin Valley of California. (2021). Paediatric and Perinatal Epidemiology. Ha, S., et al.
- Annual Report on the Conditions of Children in Orange County. Orange County Children's Partnership.
- Community Health Improvement Plan for Los Angeles County. Los Angeles County Dept. of Public Health.
- Key Indicators of Health by Service Planning Area. (2017). Los Angeles County Dept. of Public Health.
- Live Well San Diego Report Card on Children, Families, and Community. The Children’s Initiative.
- Pathway to Progress: Indicators of Young Child Well-Being in Los Angeles County. First 5 LA.
- Santa Monica Youth Wellbeing Report Card. Santa Monica Cradle to Career.
- Youth Need Data. Get Healthy San Mateo County.
- More Data Sources For Low Birthweight and Preterm Births
- 2022 KIDS COUNT Data Book: State Trends in Child Well-Being. Annie E. Casey Foundation.
- California Strong Start Index. First 5 Association of California & Children’s Data Network.
- CDC WONDER. Centers for Disease Control and Prevention.
- Maternal and Infant Health Assessment (MIHA). California Dept. of Public Health & University of California San Francisco.
- National Survey of Children's Health. Child and Adolescent Health Measurement Initiative.
- PeriStats. March of Dimes Perinatal Data Center.
- Pregnancy Risk Assessment Monitoring System (PRAMS). Centers for Disease Control and Prevention.
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