juney It very much depends on the exercise. You need to be fit and healthy to have a smooth birth, but some types of exercise hinder you.
Walking is good, weight and resistance training is good, aerobics is bad. According to the following video, having your heart beat elevated day in day out makes your body think you are in physiological stress and you don't release an egg.
It sort of makes sense. The only exercise Victorian ladies got was a daily walk around the park and they usually managed to produce six or seven sprogs often into their forties. And if you look at videos of hunter gatherer societies, the women walk loads (to fetch watch and firewood and collect berries and nuts) but they never ever run anywhere. It's painful to run without a bra anyway and they don't wear one! It's possible that we've evolved to think of running and elevated heart-rate as a sign that we're in a dangerous environment where we are constantly running from wicked predators. Not a good environment to bring up a baby in.
Same thing goes for diet. Losing weight helps you conceive (fat gives off estrogen over and above what is produced by the ovaries so you end up with the wrong estrogen-progesterone ratio). But starving yourself makes your body think you are in an unfavourable environment for babies. So you need to make sure you are eating at set times during the day, so your reptile brain doesn't think there is a famine on.
I've lost two stone doing timed eating (where I eat only during a set ten hour period) and the period covering the "fast" is largely when I'm asleep - just stop eating at 6 p.m. and start again at 8 a.m the next morning. The best article about this method is the following one:
jamesclear.com/the-beginners-guide-to-intermittent-fasting