Prenatal “Shocks” and Birth Outcomes

Birth weight is often used as a rough gauge for the quality of the prenatal environment. A newborn who weighs 2500g or less (about 5.5 pounds) is considered to be “low birth weight” (LBW). At the individual level, weight alone is an imperfect measure because of confounders such as gestational length (it’s axiomatic that the less time spent in the womb, the less time there is to grow). However, at the population level, if average birth weight fluctuates, then it is an indication that something in the environment probably has changed.

Sometimes, stressful changes can be low-intensity and chronic; at other times, they can be abrupt and dramatic. Biologists, psychologists, and bioanthropologists might call these changes “stressors” or “insults.” Economists might use the term “shocks.” They’re both getting at the same idea: to what extent can harmful environmental factors affect growth and health outcomes? 

In the case of a natural disaster, the harm done can be substantial. Florencia Torche (2011) found that rates of LBW increased following the 2005 Tarapaca earthquake in northern Chile. Despite the magnitude of the earthquake (7.9 on the Richter scale), the amount of destruction was relatively limited: eleven people died, and 0.035% of the population had to temporarily relocate to shelters. This was attributed to the low population density of the region as well as Chilean preparedness and building codes to withstand earthquakes. Although the damage was not as severe as it could have been, Torche reasoned that the earthquake likely caused acute maternal stress, which in turn could affect prenatal development. 

Looking at over half a million births, Torche used maternal county of residence as an estimate of the earthquake’s intensity across different trimesters of exposure. She found that mothers who were lived in the most intensely affected regions during the first trimester were the most affected. The probability of LBW increased from 4.7% to 6.5%, while rates of pre-term births also increased from 5.2% to 8.0%. Later periods of gestation were not substantially affected, and for infants who were conceived after the earthquake, the probability of LBW returned to baseline.

Again, these outcomes seemed to result primarily from acute psychological stress stemming from the earthquake. Torche reasoned that – given the relatively low amount of damage to infrastructure – the increases in LBW and pre-term births were unlikely to have resulted from other factors such as malnutrition, infection, stress resulting from deprivation, strenuous workloads, or exposure to environmental toxins. In reality, it’s not possible to control for all of these variables entirely, but overall it seems plausible that maternal psychological stress played a substantial role in birth outcomes.

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Did the Atomic Bombs in Hiroshima and Nagasaki Affect Child Growth?

In 1967, James Wood and colleagues published a study on the growth of Japanese adolescents whose pregnant mothers were exposed to the atomic bombs in Hiroshima and Nagasaki years earlier. Of course, many people were killed by the bombs, although estimates vary somewhere between one and two hundred thousand in all. By one estimate, the mortality rate of people within one kilometer of the bomb’s hypocenter in Hiroshima was 86%. This rate dropped to 27% for people who were between 1 and 2.5 km, and to 2% for those between 2.5 and 5km. Comparable numbers were reported for Nagasaki: 88%, 34%, and 11% respectively. This study was about some of the survivors.

Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map. From wikicommons.

Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map. From wikicommons.

In all, the Wood et al. study included 1,259 seventeen-year-olds, who had annual medical examinations since 1950. They were then compared for height, weight, and head circumference by their mother’s distance from the bombs’ hypocenters. They concluded that:

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40 Years After the Second Indochina War

Today does not escape easily from yesterday.

Several media outlets have published stories in the last few days marking the 40th anniversary of the ‘end’ of the Vietnam War (although it is more accurately known as the Second Indochina War because it also involved the neighboring countries of Laos, Cambodia, and Thailand).  

Some of these stories are about families of American veterans still searching for the remains of lost loved ones.  Others are about the lingering divisions between northern and southern Vietnamese, even within the same family.

Perhaps Viet Thanh Nguyen, an associate professor of English and American studies at the University of Southern California, best summarized these accounts with his NYTimes essay “Our Vietnam War Never Ended”. He describes moving to the US as a young boy and then growing up in San Jose, California with a foot in two cultures, as well as the struggles and successes of Vietnamese and other refugee groups in the US. And despite the fact that his family members have achieved a lot, such as producing a professor at a prestigious university, he writes that their story is not a fairy tale: 

“our family story is a story of loss and death, for we are here only because the United States fought a war that killed three million of our countrymen (not counting over two million others who died in neighboring Laos and Cambodia).”

Those two themes, that the war never truly ended, and that even those who survived and succeeded later in life have stories of loss and death, are important reminders of the past’s ability to reach into the present, even after forty years of yesterdays. All wars are unique, but their most consistent feature of war is the creation of suffering, which can last for decades, perhaps even centuries. Continue reading