heart rate and Fitbit?

Here is a question for all the ladies who wear fit it's or anything that monitors your heart rate. Did you ever notice a change in you heart rate after getting pregnant, and if so how soon after? I'm wondering cause I wear a Fitbit and for the last 3 weeks my heart rate is normally 62-65 when sitting/watching tv. Well I have been trying for a baby for sometime now and I noticed yesterday that my heart rate is now between 74-81 when just sitting/watching tv. I heard that your heart rate goes up and I want to see how many if any have noticed this? Thank you ladies for any information.