DATA STORY

Percentage of preterm births

Percentage of all live births born before 37 weeks of pregnancy in San Francisco

Maternal, Child, and Adolescent Health

Part of: Maternal, Child, and Adolescent Health Epidemiology Unit

What percentage of babies were born too early last year?

Last year, 8.4 percent of babies were born too early, before 37 weeks of pregnancy.

In 2024, 1.0 percent of babies were born very early, before 32 weeks of pregnancy.

The percentage of babies who were born preterm or very preterm in San Francisco has not changed significantly for 10 years.

Data notes and sources

Data source: 

  • California Department of Public Health (CDPH) Vital Record Business Information System (VRBIS). VRBIS data include one birth certificate record for each and every baby born in California.
  • Data were analyzed by the San Francisco (SF) Department of Public Health Maternal Child & Adolescent Health Epidemiology Section.

Data notes:

  • Preterm birth is defined as live birth before 37 weeks of pregnancy. Very preterm birth is live birth before 32 weeks of pregnancy.
  • We count preterm births experienced by San Francisco residents between January 1 and December 31 of each year. 
  • The March of Dimes aims to decrease the preterm birth rate below 5.5%.  
  • Over the past 10 years in San Francisco, the preterm birth rate remained the same (about 8% of babies born preterm). 
  • San Francisco has a lower rate of preterm birth than other California counties, and a rate that is below the national Healthy People 2030 target of 9.4%.
  • Between 2015 and 2024, there were no significant improvements or decreases in the proportion of births before 37 weeks.

Data limitations:

  • Data are not shown if the number of preterm births in the group is less than 20 to protect the privacy of individual people in the group. For small groups, please see the days of pregnancy lost because of preterm birth for the group.
  • The total numbers shown here may undercount the true numbers, because we do not count preterm births that happened outside of California, in other states or countries.
  • We do not count babies delivered in San Francisco by people who are not San Francisco residents.

The table shows the percentage of babies born preterm each year with its confidence interval. When confidence intervals overlap, the difference between percentages may only be due to random chance or measurement error.

What percentage of babies were born too early by population group?

National Healthy People policy aims for the percentage of births born preterm to be below 9.4 percent in every population group.

Even though San Francisco, as a whole city, meets the national target, preterm birth risk remains above this target for several groups in San Francisco.

Preterm birth risk remains high for Black or African American (AA) people, people with housing or food issues (WIC eligible), people who smoke or have fertility or chronic health problems, such as diabetes and high blood pressure.  

As a group, people with adequate prenatal care had the lowest rate of preterm birth in San Francisco in 2022-2024:  3.5 percent. 

This line graph shows trends in the percentage of babies born too early over 3-year periods by population group. Click on 'Preterm' or 'Very preterm' to see data for births before 37 weeks or data for births before 32 weeks of pregnancy. Use the filter on the left of the graph to select one or more population group(s). For bar graphs comparing 3-year preterm birth rates by population group, see the linked disparities page.

Data notes and sources

Data source: 

  • California Department of Public Health (CDPH) Vital Record Business Information System (VRBIS). VRBIS data include one birth certificate record for each and every baby born in California.   
  • Data were analyzed by the San Francisco (SF) Department of Public Health Maternal Child & Adolescent Health Epidemiology Section.  

Data notes:

  • Preterm birth rates are calculated as the number of preterm births divided by the total number of births in the group, multiplied by 100.
  • Abbreviations:  Black/AA: Black or African American. CPMC: California Pacific Medical Center; UCSF: University of California San Francisco; ZSFG: Zuckerberg San Francisco General. 95% CI: 95 percent confidence interval. Two rates are statistically significantly different if their confidence intervals do not overlap.
  • Race and ethnicity were self-reported by the parent(s) and grouped by the California Department of Public Health, which separates multi-race Hispanic and single race Hispanic groups. 
  • Quality of prenatal care was checked using the Kotelchuck index 
  • The birth record notes if the birthing parent was ever diagnosed by a doctor with health conditions including high blood pressure, diabetes, and infections before or during pregnancy.  

Data limitations:

  • Data are not shown if the number of preterm births in the group is less than 20 to protect the privacy of individual people in the group. For small groups, please see the days of pregnancy lost because of preterm birth for the group.
  • We do not count babies delivered in San Francisco by people who are not San Francisco residents. 
  • The numbers shown here may undercount the true number of preterm births because we did not count preterm births delivered by San Francisco residents outside of California, in other states or countries. The birth record data may be incomplete because of health conditions that were not diagnosed. 

Use the table under the line graph to find out if the risk of preterm birth got better or worse for the selected group. Two percentages are significantly different if their confidence intervals do not overlap.

Where in San Francisco is the risk of preterm birth?

National Healthy People policy aims for the percentage of preterm birth to be below 9.4 percent everywhere, no matter where people live.

This map shows the percentage of births born preterm in San Francisco by zip code and 3-year period. Use the filter to select a 3-year period. For population-specific maps, see the linked page about preterm birth disparities.

Data notes and sources

Data source:

  • California Department of Public Health (CDPH) Vital Record Business Information System (VRBIS).  VRBIS data include one birth certificate record for each and every baby born in California.   
  • Data were analyzed by the San Francisco (SF) Department of Public Health Maternal Child & Adolescent Health Epidemiology Section.  

Data notes:

  • Preterm birth rates are calculated as the number of preterm births divided by the total number of births in the group, multiplied by 100. 
  • Abbreviations:   Black/AA: Black or African American.  CPMC: California Pacific Medical Center; UCSF: University of California San Francisco; ZSFG: Zuckerberg San Francisco General.  95% CI:  95 percent confidence interval. Two percentages differ significantly if their confidence intervals do not overlap.
  • Percentages with confidence intervals that do not contain 9.4 are significantly different from the national Healthy People target of 9.4 percent.
  • Race and ethnicity were self-reported by the parent(s) and grouped by the California Department of Public Health, which separates multi-race Hispanic and single race Hispanic groups. 
  • Quality of prenatal care was checked using the Kotelchuck index 
  • The birth record notes if the birthing parent was ever diagnosed by a doctor with health conditions including high blood pressure, diabetes, and infections before or during pregnancy.  

Data limitations: 

  • Data are not shown if the number of preterm births in the group is less than 20 to protect the privacy of individual people in the group. For small groups, please see the days of pregnancy lost because of preterm birth for the group.
  • We do not count babies delivered in San Francisco by people who are not San Francisco residents. 
  • The numbers shown here may undercount the true number of preterm births because we did not count preterm births delivered by San Francisco residents outside of California, in other states or countries. The birth record data may be incomplete because of health conditions that were not diagnosed.  

The table next to the map shows the percentage of babies born preterm by zip code. Percentages with confidence intervals that do not overlap are significantly different.

More information

See linked pages about preterm birth in San Francisco