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I recently looked back in my family history and realized that my grandfather was born in 1917. That means he lived through the influenza pandemic of 1918-1919 (often referred to as the Spanish Flu) that killed 50 million people around the globe. Though my grandfather was born before the pandemic, the simple fact that he lived through it got me to wondering whether babies born during that pandemic suffered any enduring health effects that continued during their lifetimes. It turns out, the answer to that question is “yes”. Let me tell you more.
Fetal Origins Hypothesis
In 1995, a scientist named David Barker wrote: “The fetal origins hypothesis states that fetal undernutrition in middle to late gestation, which leads to disproportionate fetal growth, programmes later coronary heart disease.” In other words, the environment in which a fetus develops has an effect on their health later on in life.
There have been many attempts to study the fetal origins hypothesis, but it is difficult to isolate and discern which environmental causes have what effects on fetal development. That is why scientists have traditionally looked to famines or pandemics to figure out the answer. Famines and pandemics occur at particular points in time making it easy to compare fetal development and growth into adulthood at that time with other more “normal” time periods. The influenza pandemic of 1918-1919 was an ideal slice of time to study because data suggested that women of child-bearing age were especially vulnerable to this particular strain of the virus.
The Influenza Pandemic of 1918-1919
Studies of the 1918 influenza pandemic have found that people born during that time have endured negative health effects that became apparent later in life. One study published in 2006 in the Journal of Political Economy called “Is the 1918 Influenza Pandemic Over? Long-Term Effects of In Utero Influenza Exposure in the Post-1940 U.S. Population” found that babies who were born during the pandemic, over their lifetimes, had lower educational attainment, lower income, lower socioeconomic status, higher rates of disability, and higher usage of welfare programs. It was also suggested that this population suffered higher rates of schizophrenia, diabetes, stroke, trouble hearing, trouble speaking, and trouble walking.
Furthermore, a 2010 study called “Lingering Prenatal Effects of the 1918 Influenza Pandemic on Cardiovascular Disease” published in the Journal of Developmental Origins of Health and Disease found that fetal exposure to the 1918 flu led to higher rates of cardiovascular disease later in life. Researchers also found reductions in adult height in this population.
Additionally, a 2016 working paper for the National Bureau of Economic Research entitled “Does In Utero Exposure to Illness Matter? The 1918 Influenza Epidemic in Taiwan as a Natural Experiment” found that babies who were born during the epidemic were shorter in stature during their childhood and adolescent years. The researchers also found that, in older age, this population suffered more serious health issues such as “kidney disease, circulatory and respiratory problems, and diabetes.”
How can the environment a fetus experiences in utero cause health problems later in life? It’s a pretty simple concept actually. When the fetus experiences any type of physical stress, like maternal malnutrition or infection, fetal blood and nutrient flow diverts to the brain instead of other organs in order to preserve the life of the fetus. Unfortunately, this leaves other organs lacking in vital oxygen and nutrients and sets those organs up for problems later in life.
It has been suggested that the developmental timing of fetal stress affects different organs because certain organs develop early in gestation and others develop later. For example, the heart is one of the first organs to begin to form, therefore if fetal stress is experienced earlier in a pregnancy there could be a higher probability of heart disease later on in life. Likewise, the gastrointestinal (GI) system also develops relatively early in a pregnancy. Fetal stress during the stage of GI system development could lead to diabetes or other metabolic disorders. On the other hand, the kidneys are developed later in the pregnancy. Fetal stress experienced in the later stages of gestation could set the kidneys up for problems in later life.
Implications for COVID-19
It remains to be seen what type of fetal stress is being experienced during our current pandemic. There is much we still don’t know. What we do know is that, according to the Centers for Disease Control, pregnant women may be at increased risk for serious complications from infection with SARS-CoV-2 (the virus that causes COVID-19). Additionally, it has been shown that COVID-19 infection invades the blood vessels of the placenta (the temporary organ that provides oxygen and vital nutrients to the fetus), causing blood clots and impeding blood flow between mother and fetus. Whether or not this fetal stress will cause health issues later in life remains to be seen.