In my experience motion soothes babies. Before my babies were born, they were generally more active when I was not moving. I found the typical time for my babies to start bouncing around is in the evening when you lay down to sleep. So perhaps the exercise that your wife is doing is the right motion to lull the fetus to sleep.
I was curious and did a little looking around for you. On a parenting forum I have visited in the past a number of women noted changes in fetal activity after exercise, some had mentioned to their physicians who were reportedly unconcerned.
Personally, I recall my daughter moving more during and after exercise when I was pregnant. However, I was doing prenatal yoga and paying more attention to my body so it could just be my perception.
I found one study indicating that changes in fetal movement was normal following exercise http://www.ncbi.nlm.nih.gov/pubmed/9154415 .
If your wife is concerned I would recommend discussing this with her physician or midwife.
answered 28 Mar '11, 15:18