Overheating is the chief and main risk. Heat stroke in the mother can be deadly to the fetus. Keeping cool is vitally important.
Related to that is keeping hydrated; ideally you should sip water or another fluid frequently while doing aerobic exercise. If that's not possible then make sure you have a lot of water to drink both before and after the heavy exertion.
Again related to keeping cool, pregnant women have hyper-sensitive skin. They are more vulnerable to getting sunburnt and heat rashes. Wear sunblock and avoid jogging in the midday sun!
It goes without saying, but anything that exhausts the mother isn't really good for the fetus. Exercise in pregnancy should leave you feeling happily tired, not shattered. Other things to be careful about are warming up slowly to protect ligaments (they get a bit stretchy in pregnancy), and don't do contact sports or anything with a high risk of falling. Cycling may be ok, but your balance may be affected by hormones and the extra weight, so be careful about it.
Related to that is keeping hydrated; ideally you should sip water or another fluid frequently while doing aerobic exercise. If that's not possible then make sure you have a lot of water to drink both before and after the heavy exertion.
Again related to keeping cool, pregnant women have hyper-sensitive skin. They are more vulnerable to getting sunburnt and heat rashes. Wear sunblock and avoid jogging in the midday sun!
It goes without saying, but anything that exhausts the mother isn't really good for the fetus. Exercise in pregnancy should leave you feeling happily tired, not shattered. Other things to be careful about are warming up slowly to protect ligaments (they get a bit stretchy in pregnancy), and don't do contact sports or anything with a high risk of falling. Cycling may be ok, but your balance may be affected by hormones and the extra weight, so be careful about it.