Global warming lowers birth weights
A University of Utah study finds that along with melting glaciers and increasing wildfires, low birth weight babies are also a consequence of global climate change.
In the first of its kind study, a two-year project led by University of Utah geography professor, Kathryn Grace PhD, examined the relationship of precipitation and temperature on infant birth weight across 19 African countries.
Grace and her team used detailed climate data together with extensive health data to define the effects of climate change on birth weight in developing worlds. Her findings show that a pregnant woman's exposure to reduced precipitation and an increased number of very hot days, results in lower infant birth weights.
"Our findings demonstrate that in the very early stages of intra-uterine development, climate change has the potential to significantly impact birth outcomes. While the severity of that impact depends on where the pregnant woman lives, in this case the developing world, we can see the potential for similar outcomes everywhere."
Kathryn Grace PhD, Profesor of Geography, University of Utah
Low birth weight is the most reliable measure of whether a pregnancy has been negatively affected by an external factor. This is especially true in rural countries having no routine doctor visits or over the counter pregnancy tests to let mothers' know exactly when they become pregnant. The World Health Organization defines low birth weight as any baby born under 2,500 grams which is equal to 5lb 8.184912oz.
Low birth weight infants are more susceptible to illness, more likely to develop disabilities, less likely to reach education and income levels as high as infants born within a healthy weight range, and face a higher risk of death.
Consequently, the financial burden of a low birth weight infant can be significant to a family, their community and their country. In developing countries where support services are less common and physical disability is considered a social stigma, low birth weight can lead to even greater difficulties.
In 2013, Grace and colleagues reviewed health data collected by the United States Agency for International Development which reflected each country's food growing seasons, temperature and rainfall. They also collected farming and livelihood information from the U.S. Agency for International Development's Famine Early Warning System program, and included precipitation data from the Climate Hazards Group InfraRed Precipitation.
In total, the team examined nearly 70,000 births in 19 African countries between 1986 and 2010 and matched these births with seasonal rainfall and air temperatures, as well as variables describing the mother's education level and whether there was access to electricity at home.
Their overall findings were reported in the journal Global Environmental Change. This is the first time research has used fine-resolution precipitation and temperature data alongside birth data to create an analysis of the impact of weather on birth weight.
To generate precipitation records for each birth, the team calculated the average precipitation for a given month within 10 km of the child's birth location. This was done for each month in the year prior to a child's birth, then re-identified as the appropriate trimester preceeding the actual birth date.
The same method was used to generate temperature records for each birth. The team first calculated the maximum daily temperature for a given calendar day within 10 km of a child's birth location. From there, the number of days in each birth month where the temperature exceeded 105 F and 100 F as the maximum daily temperature were presented in each trimester.
The results show that an increase of hot days above 100 F in any trimester corresponds to a drop in baby birth weight. In fact, just one extra day over 100 F in the second trimester corresponds to a decrease of 0.9 grams in baby weight. This held true when the temperature increased to 105 F - and baby weight dropped further.
Conversely, higher amounts of rain during any trimester resulted in higher birth weights. On average, a 10 mm increase in precipitation during a particular trimester corresponds to an increase in birth weight of around 0.3 - 0.5 g.
"While these results are dependent on trimester and location, the data shows that climate change – a combination of increased hot days and decreased precipitation – correlates to lower birth weight," added Grace.
"In the end, services we invest in to support developing countries won't reap the same level of benefits as long as climate change continues. Services such as education, clean water efforts and nutrition support won't be as effective. We need to work faster and differently to combat the evident stresses caused by climate change."
• Temperature and precipitation may impact birth weight outcomes.
• Maternal nutrition experiences may link birth weight and climate variability in poor countries.
• Birth weight outcomes are impacted by changes in the number of hot days and precipitation amounts.
• The linkages between birth weight and climate exist apart from socio-economic variabilities.
This paper examined the relationship between birth weight, precipitation, and temperature in 19 African countries. We matched recorded birth weights from Demographic and Health Surveys covering 1986 through 2010 with gridded monthly precipitation and temperature data derived from satellite and ground-based weather stations. Observed weather patterns during various stages of pregnancy were also used to examine the effect of temperature and precipitation on birth weight outcomes. In our empirical model we allowed the effect of weather factors to vary by the dominant food production strategy (livelihood zone) in a given region as well as by household wealth, mother's education and birth season. This allowed us to determine if certain populations are more or less vulnerable to unexpected weather changes after adjusting for known covariates. Finally we measured effect size by observing differences in birth weight outcomes in women who have one low birth weight experience and at least one healthy birth weight baby. The results indicated that climate does indeed impact birth weight and at a level comparable, in some cases, to the impact of increasing women's education or household electricity status.
The other authors are Frank Davenport, Heidi Hanson, Christopher Funk and Shraddhanand Shukla.
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