Hi Kara - First off, just let me say that I'm NOT a doctor, I'm just passing on what I've learned from one of my reproductive endocrinologists (RE).
At a recent conference, one of the ladies asked the RE about the possible side effects of Clomid, and the doc answered that there's evidence that it may (MAY) cause the endometrial lining to be not as thick (the doc also said that it could also cause the multiple pregnancy). That's all that the doctor said, so I can't really elaborate anymore than this.
As for the progesterone, I know that when I was pregnant (IVF/ICSI twins), the progesterone that I was on (intramuscular injection) was to ensure the lining of the uterus remained "thick" and was supporting my babies okay (since there was no corpus luteum on the ovary to make the progesterone hormones).
With my own personal experience, I don't know about the preeclampsia link with Clomid or progesterone. (I didn't conceive on clomid, and my perinatologist was okay with me being on progesterone injections 10 1/2 weeks into my pregnancy, and I didn't have preeclampsia until post-partum.)
I'd definitely bring it up to my doctor, Kara. Any concerns or questions, I hope that your doc answers it to your satisfaction and that you're fully comfortable with the answer he/she gives you. Best of luck and I hope that it all goes well and that you get a "+" test really soon! [:)]
Norlisa Keffer(35), Washington State Coordinator / Moderator, Mothers of Multiples / Co-Moderator, Trying to Conceive
DH, Gordon (37)
Joseph/Josephine Our Angel in Heaven (9/16/02)
Mary Frances and Samuel (a.k.a. Frankie and Sammy) 38 2/7 weeks, 5/26/03, no preeclampsia during pregnancy, mom severe high blood pressure problems post-partum