Does stress have an impact on pregnancy?

Yes. Stress (in excess) is not good for any bodily function, including pregnancy. Pregnancy by itself is a very severe stress on the body. Try to eliminate whatever stress you can to insure an enjoyable and successful pregnancy.
Usually Not. Stress - both physical and emotional - creates physiologic changes. Mildly elevated heart rate, respiratory rate , and blood pressure can last a few minutes or hours. Additional stress can exacerbate pre-existing conditions such as chronic hypertension. Most studies show no increase in poor pregnancy outcomes due to stress.