Thanks for your comment. No, I don't overheat as I only run at dusk - or in airconditioning!

I do have to correct your comment about maintaining a HR under 140 bp. That recommendation was retracted by the American College of Obstetricans and Gynecologists in 1994 (almost 10 years after they published it), and is unfortunately still quoted regularly. They new guidelines have eliminated using HR as a measure of exertion altogether.

Researchers now advise on a self-perceived level of exertion. For example, staying between 12 to 14 on the Borg index (a measure of perceived exertion used by athletes to measure exercise intensity) to maintain fitness when pregnant.