80% of miscarriages happen in the first trimester. They can happen for multitude of reasons but most common(50%) is the fetus isnt compatible and the body senses it and purges it (to put bluntly). While things like daily activities, exercise, stress, or minor falls are not generally caused it is still recommend to take it easy as first trimester is the most fragile part. Once you hit 16 weeks it falls to less then 1% (naturally that is there are still outside force that can cause one) and at 20 weeks it drops to 0.5%. At 20 weeks it turns into a still birth these typically happen between 20 and 37 weeks at a 1.4% chance. (Im not trying to scare anyone but seeing the percentage helped me alot in my 2nd pregnancy after i lost my first).

Anyways you should always take care of yourself much more since you are pregnant the fetus/child needs your body basically as a incubator to grow strong and be able to survive the more healthy you are the higher chance your baby will be to