As global temperatures increased by 0.5 °C to 1 °C during the last half century, the number and severity of heat waves also increased. Headlines pronounced the huge mortality tolls: more than 1000 deaths in the US East Coast and Midwest heat wave of July 1995 and up to 70 000 in the 2003 European heat wave.
Unreported, unseen, and not well appreciated is the association of heat waves with pregnancy outcomes. The physiology of pregnancy has already engaged the cardiovascular responses that are activated to cool the body, increasing cardiac output and decreasing peripheral vascular resistance, so hyperthermia is more frequent and severe in pregnant women. The fetal circulation is also compromised, as maternal blood flow is shunted to the skin for cooling. Not surprisingly given these biological effects, elevated temperature was the first identified teratogen based initially on animal observations.