Babies born at low birth weight (defined as 2,500 grams - approximately 5.5 lbs. - or lower) are at an increased risk of infant death as well as many long-term disabilities and developmental delays.
Low birth weight is a big public health challenge in much of the US, as 8.0 percent of babies born in 2014 were born at low birth weight. While the national prevalence rate was 7.0 in 1990, it peaked at 8.3 percent in 2006, and has been moderately falling in more recent years. The Center for Disease Control and Prevention's Healthy People 2020 Program has set a target for the US of 7.8 percent by 2020.
The prevalence of very low birth weight (defined as 1,500 grams - approximately 3.3 lbs. - or lower) has remained steady over the same time frame, hovering between 1.4 and 1.5 percent.
Mothers who are most likely to have a baby born at low birth weight are those who smoke during pregnancy, are under age 20, are age 40 and older, are in poor health, are receiving inadequate prenatal care, are pregnant with twins or triplets (or more), or have certain uterine abnormalities.
Geographically, Appalachia, the Rocky Mountains, and the South have high rates of low birth weight. Considering state-level data, Mississippi, Louisiana, and Alabama had the highest rates in 2014 at 11.3, 10.5, and 10.1 percent respectively. The map below shows county-level prevalence from 2010-2014, with counties with a high prevalence of low birth weight in dark red. Jackson County, CO had the highest rate at 38.5 percent.
Zoom in, pan around, and click on your county to see the rate.
A common reason for low birth weight is preterm birth (defined as birth before 37 weeks of gestation). Many risk factors for having a low-birth-weight baby are the same for having a preterm birth.
In 2014, 9.6 percent of infants in the US were born preterm. Just as with low birth weight, rates of preterm births varied by maternal characteristics and by geography. The map below shows county-level prevalence from 2010-2014, with counties with a high prevalence of preterm births in dark red.
Zoom in, pan around, and click on your county to see the rate.
Provide evidence-based tobacco cessation and prevention programs for pregnant women.
Unfortunately, many smoking cessation programs are designed largely for men, and do not address the unique needs of pregnant women, e.g. not being able to take medication for withdrawal symptoms (Shore & Shore, 2009). Combining cell phone- and internet-based interventions, such as SmokefreeMOM, with traditional programs have shown to increase quit rates. Integrating smoking cessation into other prenatal care would provide a convenient option for expectant mothers. In addition, efforts should be made to increase public awareness of the harmful effects of smoking during pregnancy, while recognizing that smoking during pregnancy is most often because of addiction, not moral failing - most women who smoke during pregnancy want to quit. Cigarette smoking during pregnancy is a well-known cause of low birth weight, even after controlling for other factors. An estimated 8% of mothers smoked during pregnancy in 2014 (KIDS COUNT Data Center, 2014). Ensuring that pregnant women have free and convenient access to smoking cessation programs, and minimizing stigma from participation, is paramount to addressing low birth weight. Of course, helping people stop smoking before they become pregnant, and discouraging people from starting to smoke in the first place, is most cost-effective in the long run.
Ensure that pregnant women get appropriate nutrition.
Increase efforts to build nutritional counseling into prenatal care, and continue programs that offer nutritional support to low-income expectant mothers such as the WIC program. Overweight and obesity increases women's risk of delivering early, which then increases risk of low birth weight (McDonald et al, 2010). Health care providers generally recommend that a woman of normal weight gain 25 to 35 pounds during pregnancy, and women who gain less than 22 pounds are twice as likely to have a low-birth-weight baby (Dickinson, 2004). Consuming 400 micrograms (mcg) of folic acid is recommended, however researchers have found that when a poorly-nourished woman becomes pregnant, vitamins are not enough to reduce her odds of having a low-birth-weight baby, even if taken very early in pregnancy (Goldenbert & Culhane, 2007).
Ensure that pregnant women have access to prenatal care.
Timely prenatal care is extremely important, however an estimated 16.6% of pregnant women in 2011 did not receive prenatal care in their first trimester (CDC Pregnancy Risk Assessment Monitoring System). By starting prenatal care as soon as possible, health professionals can identify and treat specific conditions that would lead to any complications, as well as refer women to programs and treatment services for tobacco and illicit drug use (Dickinson, 2004; Ramakrishnan, 2004).
Ensure that pregnant women have access to broader medical services, such as dental and mental health services.
There is growing research that health care strategies that only focus on pregnancy are not sufficient, as they cannot make up for a lifetime of disadvantage and compromised health. Tooth decay and gum disease are infections that can be carried into the bloodstream, and therefore increase women's odds of having preterm and low-birth-weight babies (Shore & Shore, 2009). Also, studies have linked depression during pregnancy to an increase in the percent chance of preterm labor and low birth weight (Grote et al, 2010).
Continue efforts that address related social and environmental risk factors.
Social and environmental factors such as poverty, teen pregnancy, obesity, adult-onset diabetes, high blood pressure, and cardiovascular disease are all associated with a higher percent chance of having a low birth weight baby (Shore & Shore, 2009). Efforts that improve these social and environmental factors can indirectly improve low birth weight outcomes.
Support ongoing research on the causes of low birth weight.
Much is still unknown as to the direct and indirect causes of low birth weight, but new research is beginning to shed light on other factors such as neighborhood factors that pose health risks, and paternal health and environmental exposures that affect seminal fluid (Reichman, 2005).
When examining the Low Birth Weight and Preterm Births maps above, the parishes in Northwest Louisiana are clearly more red than the neighboring counties of Texas and Arkansas.
Let's look at the Low Birth Weight map again, zoomed in to Louisiana:
This difference is even starker in the Preterm Births map, zoomed in to Louisiana:
Informed by the policy recommendations by experts listed above, and using demographic methods for comparison, we investigated three possible factors that may have contributed to the high prevalence rates that parishes in the Pelican State experienced compared to neighboring counties in other states:
While data on births to mothers who reported smoking during pregnancy is only available at the state and national level, Louisiana does not stick out here. Louisiana had a share of births to mothers who reported smoking during pregnancy of 7 percent in 2014, compared to 4 percent in Texas, an 8 percent national average, and 15 percent in Arkansas. While county-level analysis cannot be performed here, from the statewide rates it does not seem as if differences in smoking rates among mothers is a big contributor to the stark differences in rates of low birth weight and preterm births on the LA-TX and LA-AR borders.
Fortunately there is good county-level data on the general adult smoking rate. While the rates for the Arkansas and Louisiana bordering counties/parishes are very similar in 2015 (18-24 percent for Northwest Louisiana parishes bordering Arkansas, and 20-21 percent for Arkansas counties bordering Northwest Louisiana), the Texas counties on the Northwest Louisiana border have slightly lower smoking rates (16-18 percent) than the rates of Northwest Louisiana parishes bordering Texas (20-22 percent) (Data from CountyHealthRankings.org). It's possible that second-hand smoke might be a contributor to the differences in low birth weight, as those were more visible along the TX-LA border than the AR-LA border, and not so much a contributor to differences in rates of preterm births. What we have here is correlation - more rigorous hypothesis testing is needed to find causation.
Just as with data on births to mothers who reported smoking during pregnancy, data on when mothers started prenatal care (or if they had any prenatal care at all) is only available at the state and national level. Among the three states, Louisiana actually has the lowest rate of births to women receiving late or no prenatal care in 2014 at 7 percent, compared to 9 percent for Arkansas and 10 percent for Texas (Data from KIDS COUNT Data Center, 2014). The state-level data, while very aggregated, suggest that there's something else going on.
It is well established that low birth weight and preterm births are highly correlated with various demographic characteristics of the mother, such as age and race, and even education level and marital status.
Could it be that new mothers in Northwestern Louisiana have significantly different demographic characteristics from those of new mothers in neighboring counties across the state border?
To answer this, we looked at the county-level data from the 2011-2015 American Community Survey question "Have you given birth to any children in the past 12 months?" to give us information about new mothers in 2010-2014, the time frame for which we have data on low birth weight and preterm birth prevalence.
There are slight differences in the percentage of new mothers who are under age 20, percentage of new mothers who are age 40 and older, and percentage of new mothers who are Black or African American. Age-wise, Louisiana mothers are in the middle: the share of new mothers who are teens is highest in the neighboring Arkansas counties, and lowest in the Texas counties. Conversely, the share of new mothers age 40 or older was highest in the neighboring Texas counties, and lowest in the Arkansas counties.
However, the rates of low birth weight and preterm births for teen, older, White, and Black mothers are all higher in the Louisiana parishes. For example, the aggregated rate of low birth weight for teen mothers in Cass, Marion, Harrison, Panola, and Shelby counties (in Texas) was 9.0 percent, compared to 15.2 percent in neighboring Caddo, De Soto, and Sabine parishes (in Louisiana). Similarly, the aggregated preterm birth rate for older mothers in Miller, Lafayette, Columbia, and Union counties (in Arkansas) was 13.3 percent, compared to 22.8 percent in neighboring Caddo, Union, Claiborne, Webster, and Bossier parishes (in Louisiana). Likewise, low birth weight and preterm birth rates were higher for both Black and White mothers in the Louisiana parishes than for the same groups in neighboring counties.
The small magnitude of the differences in the age structure and racial composition of new mothers, and the difference in higher rates of low birth weight and preterm births within age and race groups, suggest that a difference in demographics is not what's driving the stark differences seen in the maps.
EXPLORE MORE:
Find out more about CDC's Healthy People 2020 Program and their national targets.
Data came from CDC's Health Indicators Warehouse, formerly at www.healthindicators.gov. Site was taken down on April 15th, 2017. Data will eventually be available on HealthyPeople.gov.
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