My crown came off and I'm 5 weeks pregnant. Not sure what is the best thing that could be done?

HI:You should go to a dentist to try to recement the crown ASAP.  The longer you wait, the higher the possibility of the crown not fitting.Best,Dr. Maddhi

I would recommend to get into your dentist to have a look. Crowns can come off for a number of reasons. Hopefully this was just a fluke and it can be simply put back on. However, sometimes there are cavities or broken tooth below that causes them to come off. Regardless it is important to have this taken care of in your second trimester or as early as possible as treatment during pregnancy is safe but can become more difficult as you progress. Also, issues such as pain or infection that could come up by doing nothing can be harmful to your developing baby

If your crown is out you need to see a dentist ASAP to prevent further damage & possible infection. A dentist will evaluate your tooth & crown, & recement it if possible or advise another treatment. 

Even though you're 5 weeks pregnant, you can still have the crown recemented. It might last but, then again, it might not depending on how much tooth is remaining. Dental work, like root canals or anything else extensive should be postponed until the 2nd trimester unless it's a true emergency situation. I would say to try and recement the crown and see what happens.