Ditto on the pennyroyal and ephedra. Peppermint, Chamomile and Raspberry leaf are all fine during pregancy. You just can't get enough raspberry leaf during this time. The more the better.
Raspberry leaf tones the uterus.
Here's some other herbs you should avoid:
(all of above herbs are either abortificants, uterine stimulants or have high content of alkaloids)
many essential oils (stick with peppermint only)
I think I would avoid hops as well, but can't quite remember why.
Here's a simple recipe you can make that's nutritious and delicious, with lots of calcium:
2 parts raspberry leaf
1 part peppermint
1 part nettles
1/2 part calendula
1/8 part hibiscus
(other good optional include dandelion leaf, calendula, rose hips & oatstraw)