I ask my dr today about running. She told me to start off easy and try not to let my pulse get above 120. Because your blood will stop going to your uterus and to your other organs.
uhhh... I know your just repeating what you were told but this is not true AT ALL.... in fact its the opposite. Blood and oxygen flow to your uterus and baby before being distributed to your own body. If you read pregnancy fitness articles they mention this as a reason why you must must must warm up and cool down. Its much easier to pull a muscle or injure yourself because everything is going to your baby. check out this article http://babyfit.sparkpeople.com/articles.asp?id=802
Edit: its pretty widely accepted these days that trying to stay under a certain heart rate is and outdated practice and doesn't do anything for you. "In the past, experts suggested monitoring your heart rate during exercise, similar to how you would when you are not pregnant. However, new research suggests that heart rate isn't an accurate way to measure intensity during pregnancy. Accordingly, the ACOG has lifted the restriction of the heart rate cap of 140 beats per minute.
When you're pregnant, your heart rate is already increased, and it is more sensitive to changes. For example, light walking may make you feel winded when you used to be able to jog. Experts now suggest using the Rate of Perceived Exertion (RPE) Scale, also called the Modified Borg Scale. This scale ranges from 1 to 10, and is a self-assessment. When pregnant, you should exercise between level 4 (Somewhat hard) and level 6 (Hard)."