Heatwaves are associated with preterm birth. Usually education is seen as protective in health outcomes. Births to women who are black are at higher risk of preterm birth.
But in examining the 3-way interaction, we find that heatwaves of 7 day duration, defined as mean high heat index in degrees C, are associated with higher risk of PTB in births to college educated women who are Black. The effect is exacerbated for heatwaves of higher heat index.
Caveats, small N (cases), rare exposure (heatwaves).
Research done in Minnesota, 1998-2005, and submitted for publication to the IJERPH.