Many dental specialists are reluctant to use any kind of IV sedation during pregnancy. It is really used as a very last resort. There needs to be communication between your dental specialist and your OB/GYN and family physician to effectively examine the risks associated with your particular case.
My advice would be to talk to your OB/GYN or family physician about this and have them coordinate with your dentist and endodontist. There may be an interim treatment that they can do for you that would get you through to the end of your pregnancy and then you can look at having the procedure done. Extraction may also be a possibility, but again you need to coordinate all this potential treatment with your OB/GYN, family physician, general dentist and dental specialist.