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

Term low birthweight (TLBW) is a live singleton birth at full term (37 weeks) with a birthweight of less than 2500 grams (5.5 pounds).

Rate (or percent) of TLBW births was calculated by dividing the total number of TLBW births by the total number of live singleton births at full term (37 weeks gestation). We looked at rates of TLBW births 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 (2.1%). In Alameda County, the countywide rate of term low birthweight birth is 2.4%.

Reading the charts

- The dotted line across each chart shows the rate of TLBW births for all of California, which is 2.1%.

- The 95% confidence interval (CI) is the range of values that likely contains the true percent of term low birthweight 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 TLBW births by the total number of live singleton births at full term in Alameda County.

Black and Asian women had significantly higher rates of TLBW births when compared to the California Statewide rate. Black women had more than two times the rate of TLBW births when compared to White women- 4.0% versus 1.5%, respectively. In Alameda County in 2001, women in other race/ethnic groups (the "Other" category- see below) had no TLBW births.

Women who lived in block groups with median household incomes less than $40,000 had higher rates of TLBW births compared to women living in higher median income areas. Women living in block groups with less than a $27,000 median household income had a rate of TLBW birth of 3.9%, twice the rate of women living in block groups with a median household income of $75-100,000 (1.9%).

Women less than 20 years of age had the highest rate of TLBW births (4.0%). Unlike their preterm birth rate, women ages 40 and above had a TLBW births rate (2.0%) that was similar to the California statewide population.

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. In Alameda County in 2001, there were no term low birthweight births among women in the Other 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.