Is my workout routine to stressful when Im trying to get pregnant? Should I slow it down?

I have always worked out (for the past 15 years) and I consider myself in good shape. Im 30 years old. I now walk on the tread mill 4 days a week for about an hour and a half during each session. I walk about 4.2 miles per hour and at an incline of 2.0. I used to run for the same length of time with an incline at a much faster rate. But I have since taken a back seat. Will my workout regimen interfere with me trying to conceive? Am I walking for too long? I really would like to continue some type of cardio fitness while trying to conceive. I am in good health and have good blood pressure (110/70). I do not smoke and do not drink coffee. I do drink ice tea. Any advice?