I’m no expert (legal, medical, real estate, or other), but I’d start with telling the apartment complex about your pregnancy and other health conditions. It may help them take action against the smokers, but at the least it may give you more leverage if you want them to accommodate you somehow or allow you to break your lease. Pregnant mothers are naturally sympathetic and leaving this issue unresolved seems like it is not only bad PR, but might potentially be grounds for a lawsuit. Unfortunately, while I would also consider secondhand smoke to be dangerous to the baby, marijuana smoking has become so common that even if they evict the current smoking tenants or if you move to new apartments, I don’t think there’s any assurance that your new neighbors wouldn’t also smoke marijuana.
I doubt the police care about your building’s no-smoking policy. If you live somewhere where marijuana hasn’t been legalized, you might be able to have them arrested, but in today’s climate, unless they’re dealing to kids from their apartment, I doubt the police would bother.
I don’t know if it would be helpful, but here’s a study about the exposure of children to marijuana smoke in multi-unit housing:
https://pmc.ncbi.nlm.nih.gov/articles/PMC7882144/