I made it! It wasn't bad, i could definitely do another 10. The time it took me to do 16 is sadly close to my full marathon time from last spring :)
Sorry, I completely misunderstood the question. When I'm not really pushing myself, I can keep it between 150 and 160. From what I understand, the heart rate guidelines are pretty out of date and impossible to follow. I've been to three different OB practices since my first pregnancy, and all three of them said that perceived effort was more important than heart rate. They told me that as long as I wasn't gasping for breath or exercising to the point of exhaustion then I was good to go.
Thanks for this. It helps. I will keep that in mind.