This article can be accessed publicly for free and one of the authors is a leading dysautonomia expert from the Mayo, so it's an excellent article:
http://www.anesthesia-analgesia.org/cgi/content/full/104/1/166
This article does not have free public access, but your doctor should be able to access it and so you can give the information to your doctor and ask that s/he obtain a copy to help better be prepared to care for you and your baby:
Pregnancy in postural orthostatic tachycardia syndrome. Glatter KA, Tuteja D, Chiamvimonvat N, Hamdan M, Park JK. Pacing Clin Electrophysiol. 2005 Jun;28(6):591-3.
( http://www3.interscience.wiley.com/journal/118650831/abstract )
This article has free public access (you may have to create a username by registering your email address and creating a password to view the full article, but it should be free):
http://bja.oxfordjournals.org/cgi/content/full/97/2/196
Hopefully the others on the site who have actually been through this can give you more anecdotal information. But sharing those articles with your doctor should give you a starting point. If you need more basic information on POTS in general (irrespective of pregnancy) to educate your doctors, let us know. You can start with the information on our further reading page but if your docs are really interested in doing some research and have access to a medical library, there are a couple of professional texts I can recommend as well:
http://www.medhelp.org/health_pages/Neurological-Disorders/Further-Reading-on-Dysautonomia/show/696?cid=196