The danger with picking your own is that you'll have no way to know the strength of the leaves and, therefore, the dose you're taking. Look for a tea (or capsules) that are certified potency.
I second googling this, as well. I know the Hypnobabies website has some information about natural remedies, etc related to pregnancy and that RRL Tea is one of them. I used the capsules personally and had no ill effects, but, of course, it's always hard to know whether or not they actually did anything.
Also, I would look specifically at when in the pregnancy it's appropriate to use RRL. I think it's one that is good at the end, but at the beginning can be an abortive...or maybe that's something else...I dunno--look it up! Speaking as the daughter of a chiropractor, I'd say ask more questions and talk to a certified naturalist in addition.
Happy baby-cooking!