Reproductive Health Indicator:  Prematurity

Measure: Preterm birth percentage; Very preterm birth percentage; Very low birthweight birth percentage

More than a half million babies in the United States—that's 1 in every 8—are born premature each year. Some babies are so small they could fit in the palm of your hand. Prematurity is the leading cause of death among newborn babies. Being born premature is also a serious health risk for a baby. Some babies will require special care and spend weeks or months hospitalized in a neonatal intensive care unit (NICU). Those who survive may face lifelong problems such as intellectual disabilities, breathing and respiratory problems, vision and hearing loss, and feeding and digestive problems. Preterm birth is associated with half of all congenital neurological defects, such as cerebral palsy.

There are some known risk factors for premature birth, like carrying more than one baby, or infections or substance use during pregnancy. But even if a woman does everything “right” during pregnancy, she can still have a premature baby. Increases in risk of prematurity or preterm delivery have been related to exposures during pregnancy to air pollution, lead, and some solvents.

Oregon EPHT is tracking prematurity so we can begin to look more closely at the links to environmental hazards. Measures of prematurity and growth retardation used here are restricted to live singleton births to remove the effect of multiple births, which are related to prematurity.

The percentage of preterm births in Oregon is 35 percent lower than the national average. As shown in the tables, graphs and map below, from 2000 to 2006, 6.2 percent of live singleton births to resident Oregon mothers were preterm. Of those, 13 percent were very preterm, and 12.5 percent were very low birthweight. Oregon preterm births increased 37 percent between 2000 and 2001. The annual percentage of preterm births decreased to 8.9 percent between 2001 and 2005, but returned to the 2001 level in 2006.

The county rates for preterm births vary widely in Oregon from 4.6 in Curry to 9.9 percent in Morrow. This variation can largely be explained by the small number of births in rural counties. When more rural counties are compared to the five most populous counties (Multnomah, Washington, Clackamas, Lane and Marion), preterm births are 6.1 percent and 6.3 percent, respectively.

Table 1: Annual percentage and count of live singleton births to resident Oregon mothers that were preterm (less than 37 weeks gestation) by county and year.   

Table 2: Annual percentage and count of live singleton births to resident Oregon mothers that were very preterm (less than 32 weeks gestation) by county and year.   

Table 3: Annual percentage and count of live singleton births to resident Oregon mothers that were very low birth weight (less than 1500 grams) by county and year.   

Table 4: 2000–2006 percentage and count of live singleton births to resident Oregon mothers that were preterm, very preterm, and very low birthweight, by county.  

Table 5: Annual percentage and count of live singleton births to resident Oregon mothers that were preterm (less than 37 weeks gestation), very preterm (less than 32 weeks gestation), and very low birthweight (less than 1500 grams).

Graph 1: Percentage of live singleton births to resident Oregon mothers that were preterm (less than 37 weeks gestation) by county, summarized for 2000 to 2006. 

Map 1: Percentage of preterm births (<37 weeks) to Oregon mothers compared with the Oregon rate.   __________________________________________________________________________________________________

Table 1: Annual percentage and count of live singleton births to resident Oregon mothers that were preterm (less than 37 weeks gestation) by county and year.  

To protect confidentiality, percentage and counts of preterm births are not shown in cases where the number of births in the county for the year is less than ten (***). Percentages based on less than ten events (count) are considered unreliable.

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Table 2: Annual percentage and count of live singleton births to resident Oregon mothers that were very preterm (less than 32 weeks gestation) by county and year.

To protect confidentiality, percentage and counts of very preterm births are not shown in cases where the number of births in the county for the year is less than ten (***). Percentages calculated with less than ten events (count) may be unreliable.

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Table 3: Annual percentage and count of live singleton births to resident Oregon mothers that were very low birth weight (less than 1500 grams) by county and year.

To protect confidentiality, percentage and counts are not shown in cases where the number of births in the county for the year is less than ten (***). Percentages calculated with less than ten events (count) may be unreliable.

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Table 4: 2000–2006 percentage and count of live singleton births to resident Oregon mothers that were preterm, very preterm, and very low birthweight, by county.

Percentages based on less than 10 events (count) are considered unstable.

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Table 5: Annual percentage and count of live singleton births to resident Oregon mothers that were preterm (less than 37 weeks gestation), very preterm (less than 32 weeks gestation), and very low birthweight (less than 1500 grams).

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Graph 1: Percentage of live singleton births to resident Oregon mothers that were preterm (less than 37 weeks gestation) by county, summarized for 2000 to 2006.

Percentages are shown with their 95% Confidence Intervals (CI). Counties whose entire CI lies above or below the Oregon average (indicated by the dotted vertical line) have percentages that are significantly higher or lower, respectively, than the Oregon average. If the CI includes the Oregon average, the county is considered statistically similar to the Oregon average.

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Map 1: Percentage of preterm births (<37 weeks) to resident Oregon mothers, shown in three statistical categories: higher than, similar to, or lower than the Oregon rate.

Data are summarized for 2000 to 2006. Statistical significance was determined by comparing the 95% confidence interval of the county rate with the State rate.

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