burg--if this is your first baby, then from the research i've done there is no reason to have the shot until after the baby is born (unless something traumatic occurs like a car accident, in which case you could go to the hospital and have the shot), and even after birth...it's still optional!!! it is a blood product and though they screen for AIDS now, in the past there were people who contracted AIDS from it... and being Rh- myself and my husband positive, it's something i've given a lot of thought to. because we don't necessarily know the next big disease that they are not screening for now, that they will be screening for in 20 years from now.
i don't mean to scare anybody, but it is important to know what you're putting in and what you're agreeing to.
just fyi, the people who are against the shot say that in a normal birth, without medical interventions the baby's blood would not normally mix with the mother's blood...so it's a very small risk or a non-risk. and unless you are in a car accident or some other anomaly where there is a risk of blood exchange, then the shot is actually riskier.
good luck, i know it's still one of things i haven't yet decided on.