Findings - Alameda County Pilot Project - California Environmental Health Tracking Program

Preterm birth is a live singleton birth prior to 37 completed weeks of gestation (less than 8.5 months).

The rate of preterm birth was calculated by dividing the total number of preterm births by the total number of live singleton births in Alameda County in 2001. For preterm birth, we looked at rates (or percents) by maternal race/ethnicity, maternal age, and median household income, in Alameda County.

The rates are displayed in charts and tables below, in comparison to the California statewide rate (8.8%). In Alameda County, the countywide rate of preterm birth was 8.5%.

Reading the charts

- The dotted line across each chart shows the rate of preterm birth for all of California, which is 8.8%.

- The 95% confidence interval (CI) is the range of values that likely contains the true percent of preterm births within the population. The upper and lower limits of this range are indicated by the thin black lines on each bar on the chart. These are sometimes known as error bars.

- Rates (or percents) were calculated by dividing the total number of preterm births by the total number of live singleton births in Alameda County.

African American women had a significantly higher percentage of preterm birth (13.0%) than women of Asian, Latino, and White descent. Asian and White women had significantly lower percentages of preterm births when compared to the California statewide rate. These percentages were 7.6% and 7.2%, respectively.

In general, as median household income of the block group increased, the rate of preterm birth decreased. Women living in block groups with lower median household incomes (less than $40,000), were significantly more likely to have a preterm birth than women living in block groups with higher median household incomes (greater than $56,000).

Women less than 20 years of age had a significantly higher percentage of preterm births (12.6%) when compared to women ages 20-39 and to the California population as a whole. Similarly, women aged 40 and above had an increased risk of having a preterm birth when compared to women ages 20-39 and to the California population as a whole.

Definition of terms

Maternal race and ethnicity information comes from the birth certificate. We grouped them into the following categories: Asian, Black, Latino, White, and Other. The ‘Other' category included Pacific Islanders and Native Americans/American Indians. If the mother had an ethnicity of Latino or of Hispanic origin, she was placed in the Latino category.

Median Household Income was taken from the Census and is based on the block group of maternal residence at the time of birth. In the United States in 2001, the "poverty threshold" for a family of four was designated as a household income of $17,960. (http://www.census.gov/hhes/poverty/threshld/thresh01.html)

In other words, any family of four living in Alameda County with a household income of $17,960 or less was considered to be poor or living in poverty. In 2001, the median household income in Alameda County was about $56,000, roughly 3 times the poverty threshold.

Considering the higher cost of living in California compared to other parts of the U.S., we decided to categorize 150% of the poverty threshold ($27,000) as the lowest income level.

Maternal age was also obtained from the birth certificates.