Starting running whilst pregnant

I’m nearly 12 weeks pregnant and last week I started going on runs. I really want to improve my cardiovascular health so that’s why I started. I’ve been doing 1km every other day. It normally takes me like 6-8 minutes so not very long!

I saw something online about not to start running whilst pregnant, but I don’t understand why. I’m only running 1km so do you guys think it’s okay I continue? Or should I stop? Could I harm my baby by running?