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Low Birth Weight and Preterm Birth

Narrative

Disorders related to low birth weight (LBW) and preterm birth (PTB) are a leading cause of infant mortality in the United States, and particularly neonatal mortality (deaths within the first month of life). The causes of LBW and PTB are not fully known, but have been linked to maternal smoking and substance use, chronic conditions, and infections (Find more information on Low Birth Weight and Very Low Birthweight and Preterm Birth.)

In 2009, 8.31 percent of infants residing in small rural counties were LBW (weighing less than 2,500 grams, or 5.5 pounds). This was slightly higher than the LBW rate among residents of urban or large rural counties (8.15 and 8.16 percent, respectively). The greater rate of LBW for residents of small rural counties was due entirely to a greater proportion of infants born at moderately LBW (from 1,500 grams or 3.25 pounds to less than 2,500 grams or 5.5 pounds) as opposed to very LBW (less than 1,500 grams or 3.25 pounds). The proportion of infants born at moderately LBW was highest among infants both in small rural counties (6.91 percent), followed by those in large rural counties (6.77 percent), and was lowest among those in urban counties (6.69 percent). However, the difference between small rural and urban counties was less than 5 percent.

Similar to LBW, there were small differences in PTB (delivering at less than 37 weeks' completed gestation) by rural and urban residence. These differences were largely confined to infants born at the late preterm range of 34 to 36 weeks' gestation. Late PTB, for example, ranged from 8.63 percent among infants born to residents of urban counties to 8.98 percent among those in small rural counties; however, this difference was less than 5 percent. Though not at highest risk, late preterm and moderately LBW infants are still at elevated risk for mortality and morbidity particularly for developmental delays, compared to their term and normal birth weight counterparts.1,2

1 Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Division of Reproductive Health. Prematurity. November 2011. Accessed: August 29, 2012.

2 Reichman NE. Low birth weight and school readiness. Future Child. 2005 Spring;15(1):91-116.

Graphs

This image is described in the Data section.

infants born with low birth weight graph

This image is described in the Data section.

infants born with very low birth weight graph

Data

Low Birth Weight (LBW),* by Rural/Urban Residence,** 2009
Residence Percent of Live Births
Very LBW Moderately LBW Total LBW
*Low birth weight, <2,500 grams or 5.5 pounds; moderately low birth weight, 1,500 to 2,499 grams or 3.25 to 5.5 pounds; very low birth weight, <1,500 grams or 3.25 pounds.
**Urban includes all metropolitan counties regardless of size, large rural includes non-metropolitan counties with a city of 10,000 or more residents, small rural includes non-metropolitan counties without a city of 10,000 or more residents; follows the National Center for Health Statistics’ Urban-Rural Classification Scheme for Counties.
Source: Centers for Disease Control and Prevention, National Center for Health Statistics. 2009 Natality Restricted Access File with Geographic Detail. Analysis conducted by the Maternal and Child Health Bureau.
Urban 1.46 6.69 8.15
Large Rural 1.39 6.77 8.16
Small Rural 1.40 6.91 8.31
Preterm Birth (PTB),* by Rural/Urban Residence,** 2009
Residence Percent of Live Births
Very PTB Moderately PTB Late PTB Total PTB
*Preterm birth, <37 weeks’ gestation; late preterm birth, 34-36 weeks’ gestation; moderately preterm birth, 32-33 weeks’ gestation; very preterm birth, <32 weeks’ gestation.
**Urban includes all metropolitan counties regardless of size, large rural includes non-metropolitan counties with a city of 10,000 or more residents, small rural includes non-metropolitan counties without a city of 10,000 or more residents; follows the National Center for Health Statistics’ Urban-Rural Classification Scheme for Counties.
Source: Centers for Disease Control and Prevention, National Center for Health Statistics. 2009 Natality Restricted Access File with Geographic Detail. Analysis conducted by the Maternal and Child Health Bureau.
Urban 1.96 1.54 8.63 12.13
Large Rural 2.0 1.54 8.78 12.32
Small Rural 2.01 1.89 8.98 12.58