Researchers in the increasingly influential field known as fetal origins—the study of how fetal conditions affect long-term health—have to be pretty creative. Running controlled experiments on pregnant women is, after all, verboten. Still, scientists have made exciting finds in recent years by cleverly drawing on data from dramatic, naturally occurring “experiments.” By seeing what happens to fetuses when an entire population is exposed to, say, fasting, or mourning, or smog—conditions that would be deemed unethical if they were devised in a lab—we are gaining insights into how life before birth shapes life long afterward.
For quite a while, scientists have known that maternal food deprivation is bad news for fetuses, correlated with everything from coronary disease later on to skewed sex ratios at birth. (Normally, 105 boys are born for every 100 girls. But during food shortages and other times of population-wide stress, relatively more girls are born, probably because male fetuses are more fragile than female ones, and more susceptible to being miscarried.) Recent studies have uncovered new examples of this effect. The Chinese famine of 1958–61 saw male births decline sharply . Even fasting takes a toll: When Ramadan occurred very early in pregnancy, Arab mothers in Michigan were 10 percent less likely to have a son. And Muslims in Iraq and Uganda were 20 percent more likely to be disabled as adults if their mothers were in early pregnancy during the holiday .
Other new research examines the effects of national grief and trauma. Throughout the U.S., a woman’s chance of miscarrying a male fetus was higher in September 2001 than in the months before or after . The Israel-Lebanon war of 2006 offers another interesting case study, not only because it exposed mothers-to-be to trauma—4,000 rockets hit northern Israel in 33 days—but because it was so short. This meant researchers could compare the effects of wartime by trimester, and could also compare a woman’s wartime pregnancy with her other, peacetime pregnancies. Offspring of women who were in the first or second trimester during the war were more likely to be premature and underweight than their siblings. Finally, although the study did not look at Lebanon, it found that Arab women in Israel had worse birth outcomes than Jewish ones .
Not so shockingly, maternal exposure to nuclear fallout bodes poorly for those in the womb. When Swedish kids who were in utero during the 1986 nuclear meltdown at Chernobyl got to high school, the ones whose mothers lived in higher-fallout areas did worse on standardized tests than other students . Exposure to pollution matters, too. One of the more inventive recent studies involves, of all things, E‑ZPass. The toll-collection system eased traffic on New Jersey and Pennsylvania highways, improving air quality, which seems to have in turn affected fetal health. Among pregnant women living within a mile or so of an E-ZPass toll plaza, premature births fell by 8.6 percent, and low birth weight, by 9.3 percent .
 Bruckner et al., “Male Fetal Loss in the U.S. Following the Terrorist Attacks of September 11, 2001” (BMC Public Health, May 2010)