My OBs OK'd it and they're pretty conservative about meds...I've heard some providers aren't wild about it though. FWIW, I took it when preg w/ DS (I have horrendous allergies - some severe random food related ones included) and he seems fine. (yes, not a scientific study, I know, but just another anecdotal bit of info. )
I have gotten mixed messages on it as well. Even an internet search had mixed results...one site stating it has been connected to spina bifida and other defects and others saying it's perfectly safe. I personally don't take it during the first tri and the first half of the second.
It's on a list of safe drugs my OB gave me, but according to some places I've read - including here http://www.safefetus.com/ - it has "oxytocic" effects, meaning it can cause cramping and contractions. GIven I have preterm labor issues I won't take it.
Motherrisk out of Sick Kids Hospital in Toronto says it's safe, I took it a few times in the beginning when I couldn't breath or sleep, just take the lowest possible dose.
I think it also depends on what you're taking it for-KWIM?
My OB suggested the liquid Benadryl or generic store brand Diphenhydramine (sp?) as it was easy to take a half dose and then take more, another half dose, as/if needed.
I've read that you should not "double up" on Benedryl and I have read that caution should be used in 1st tri-mester.
My problems with colds, allergies and congestion (snoring) were in the 2nd and 3rd tri-mesters. Her feeling was that lack of sleep from above ailments was more detrimental to the mother/baby than any very low risk from the drug and she recommends taking it only at night or nap-time if possible just to minimize exposure and to empasize that it is only for sleep relief in her view.
I took it the last month of my 1st pregnancy, to try to help with the PUPPPs and help me sleep. It was the last thing on earth I wanted to do, but I was desperate. FWIW, it did absolutely nothing to help me. My daughter has no developmental problems I've noticed, though, so it *appears* that it didn't hurt her any.
ITA with others who wouldn't take it during the first trimester, though.