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EPA's Report on the Environment: External Review Draft

Low Birthweight



Note to reviewers of this draft revised ROE: This indicator reflects data through 2010. EPA anticipates updating this indicator in 2014.




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Choose an age group from the list. Click the legend to turn layers on or off. Hover your mouse over the display to reveal data.




  • Learn more about how to use this interactive exhibit
  • Save the complete indicator as a printer-friendly PDF
  • Download this image
  • Download data for this exhibit

Choose an age group from the list. Click the legend to turn layers on or off. Hover your mouse over the display to reveal data.

Introduction

The term “low birthweight” (LBW) is typically used for any infant weighing less than 2,500 grams (5 pounds, 8 ounces) at birth (Kiely et al., 1994). Weight is a critical health measure because LBW children are more prone to death and disability than their counterparts.

The etiology of LBW for full-term-LBW (born at and after 37 completed weeks of gestation) infants and preterm-LBW (born before 37 completed weeks of gestation) infants differs. For full-term-LBW infants, underlying causes include factors such as maternal smoking, weight at conception, and gestational weight gain, whereas for preterm-LBW infants, the etiology largely remains unexplained (CDC, 1994). Various exposures have been implicated as risk factors for full-term-LBW (e.g., maternal exposure to lead, diethylstilbestrol, occupational exposures) (Kiely et al., 1994; Sram et al., 2005). The potential effect of air pollution on LBW continues to be researched (e.g., particulate matter, carbon monoxide, ozone) (Sram et al., 2005).

This indicator presents the percentage of LBW infants born in the U.S. based on natality data reported to the National Vital Statistics System (NVSS). The NVSS registers virtually all deaths and births nationwide, with data coverage from 1933 to 2010 and from all 50 states and the District of Columbia.

The data presented are based on singleton births only. This was done to eliminate the effect of multiple births. The data are presented across three maternal age groups (under 20 years, 20-39 years, and 40 years and older). Additionally, the data are stratified and reported for preterm (less than 37 weeks) and full-term (37 weeks and over) births because of the strong association between birthweight and gestational age.

What the Data Show

As expected, the percent of total LBW deliveries among preterm births is much higher than the percent of total LBW deliveries among full-term births across each of the three maternal age categories (Exhibits 1 and 2).

In general, small differences in the percent of singleton LBW babies among maternal age categories are evident for both preterm births (Exhibit 1) and full-term births (Exhibit 2). In 2010, the frequency of LBW babies among preterm births is highest for mothers who are 40 years and older (40.8 percent), followed by mothers less than 20 years old (40.1 percent), and lowest in mothers who are in the 20-39 age group (38.0 percent) (Exhibit 1). The frequency of LBW babies among full-term births in 2010 is highest for mothers less than 20 years old (4.1 percent), followed by mothers who are 40 years and older (3.0 percent), and lowest in mothers who are in the 20-39 age group (2.6 percent) (Exhibit 2).

Among both the preterm and full-term births, black women had consistently higher frequencies of LBW babies compared to any of the other racial groups reported from 1995 to 2010. This racial pattern is evident in 2010 for all three maternal age groups. For preterm births, the difference is most apparent in the 20-39 age group, with 47.1 percent for blacks, followed by 40.8 percent for Asians/Pacific Islanders, 35.1 percent for whites, and 32.8 percent for American Indians. This same racial pattern was seen with mothers less than 20 years old, but not for mothers 40 years and older, where American Indians had a higher percent of preterm births than whites (Exhibit 1). For full-term births, this racial pattern difference is most apparent in the 40 and older age group, with 5.8 percent for blacks followed by 3.2 percent for Asians/Pacific Islanders, 2.7 percent for American Indians, and 2.5 percent for whites (Exhibit 2). This same racial pattern was seen for mothers in the 20-39 age group, but not for mothers less than 20 years old, where whites had a higher percentage than American Indians.

For preterm births, there was an increase in LBW for all races from 2009 to 2010 for mothers aged 20-39 years and 40 years and older, while slight fluctuations (subtle increases for whites, but decreases for blacks, American Indians, and Asian/Pacific Islanders) were observed for mothers less than 20 years (Exhibit 1). For full-term births, an increase in LBW was seen in blacks from 2009 to 2010 for all three maternal age groups. Fluctuations from 2009 to 2010 were seen among whites, American Indians, and Asians/Pacific Islanders by maternal age group, however. For example, for American Indian mothers less than 20 years, the percent of LBW among full-term births decreased (2.7 to 2.6 percent), increased for mothers aged 20-39 years (2.4 to 2.6 percent), and then decreased for mothers 40 years and older (4.9 to 2.7 percent) (Exhibit 2).

Hispanic women and non-Hispanic women had similar frequencies of full-term LBW babies. For example, in 2010, the percent of full-term LBW babies for Hispanic women in the three maternal age groups ranged from 2.3 to 3.3 percent compared to a range of 2.6 to 4.4 percent for non-Hispanic women (Exhibit 2). A larger difference in frequencies was seen for Hispanic women and non-Hispanic women for preterm LBW babies. For example, in 2010, the percent of preterm LBW babies for Hispanic women in the three maternal age groups ranged from 33.2 to 38.8 percent compared to a range of 39.5 to 42.3 percent for non-Hispanic women (Exhibit 1). 

Limitations

  • Complete reporting of natality indicators such as LBW may vary due to differences in the reporting requirements established by each state. In some states, the number of LBW babies may be underreported.

Data Sources

The data used for this indicator were public-use natality data (1995-2010) obtained from the Centers for Disease Control and Prevention’s (CDC’s) National Center for Health Statistics (NCHS), Division of Vital Statistics, accessed via CDC’s NCHS VitalStats (CDC, 2012) available at http://www.cdc.gov/nchs/vitalstats.htm.

 

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