Im 18 weeks pregnant, and i swallowed my dental crown, does it will harm my baby?

No, the crown will be expelled in your stool in a few days. Follow all orders from OBGYN doctor and maintain good oral hygiene. You can get a new crown now or later, just make sure the tooth is protected with a temporary crown or a new one.

It should pass without incident.

If you will pardon the pun, "It will work out all righting the end." It should pass in your stool in just a few days, and will have absolutely no affect on your child. Important that you 1) Notify your OBGyn, and 2) Talk to your Dentist to assure the tooth is not infected and is appropriately treated to make sure to reduce extent of treatment going forward. Happy Baby!