I am in this boat. As always, its best to speak with your own doctor, I'm just relaying my experience.

At the beginning of the year, I started training for a marathon but halfway through decided against it after a conversation with a friend who had had trouble concieving. She had also trained for a marathon while trying to conceive and she suggested it might be too stressful on the body. I did continue with half marathon training though.

I was finally able to get an appointment with a specialist (you have to be trying for a certain amount of time before I could get a referral) and I discussed this with him. He said if you are are ovulating normally and don't have other issues (ie underweight, hormone imbalances, etc), it is perfectly fine. He had no concerns with me training.

I am racing a HM in two weeks. I am also signed up for a half Ironman next July (still hoping I won't be able to race it due to expecting though, it has a great deferral/refund policy)

Just to add- my friend was very underweight and had to gain weight to get pregnant, so in her case it was probably a valid concern. She did end up having a baby.

ETA - good luck!

I think it was Chicago Marathon 2 years ago a woman finished the race, ate a sandwich, waited for her husband to finish, then went to the hospital to give birth. Not a Dr. but I think you will be fine.

You've got to do what you're comfortable with - generally most doctors have told me that when it comes to exercise, if you were doing it before you got pregnant, it's OK to do after you get pregnant (assuming it's not something where you risked injury to your belly). You need to watch your body temperature and HR - but when you think about it, you should be keeping tabs on those sorts of things even if you're not pregnant.

My own experience - my husband & I had a tough time getting pregnant, then I had a miscarriage, so when I finally ended up with a "sticky" pregnancy, I was probably the MOST conservative pregnant person you'd ever meet. I still exercised, but in my freaked out mind, running was too jarring, so I stuck to walking, hiking, swimming. I even knew at the time that I was being hyper conservative, but it was the only tangible way for me to manage the stress/fear over losing another pregnancy. Oh, and when I was training for my first full marathon, my cycle got all jacked up, but returned to normal once I got used to that much weekly distance.

Good luck!

http://www.latimes.com/science/sciencenow/la-sci-sn-exercise-during-pregnancy-baby-brain-boost-20131111,0,4976601.story#axzz2kOUvHLqj

The rule of thumb is the same level activity you are used to is safe during pregnancy.

http://www.runnersworld.com/tag/pregnant-running

The woman who gave birth right after the Chicago marathon was also did a marathon during her first pregnancy:

http://espn.go.com/chicago/story/_/id/7084374/oh-baby-woman-runs-chicago-marathon-gives-birth

I think it was Chicago Marathon 2 years ago a woman finished the race, ate a sandwich, waited for her husband to finish, then went to the hospital to give birth. Not a Dr. but I think you will be fine.

I would absolutely do it. I wouldn't plan on a PR and allow time to take it easy if need be. Staying fit can actually have many benefits including lowering your risk for complications. I'm no doctor but i am a nurse

I thought OP was asking about training while trying to concieve.

While I do plan to continue training for the half Ironman, if I get pregnant I will not. I do not plan to do the race pregnant. I have heard the same as other have said, you can do whatever activity you did before pregnancy in most cases (there are times when you can, my running partner can't run right now because of complications). I would run a race, just not my first half ironman.