I have been serving women as a doula for over a year and just had my first encounter with what is apparently an extremely common rash in pregnant women - Pruritic Urticarial Papules and Plaques of Pregnancy. Or, much shorter, PUPPP.
I found info here: http://dermatology.about.com/cs/pregnancy/a/puppp.htm
Apparently the common treatment is steroids. But that sends up red flags for me... I am curious about what effects this might have on the baby and the mother's health.
While looking for alternative remedies, I found quite a strong consensus that Grandpa's Pine Tar soap does a superior job of diminishing the itch and clearing away the rash.

It seems that some women found other solutions, including nettle tea, dandelion root (as a tea or in capsules), flax seed oil, and aloe applied topically.
(Mothering magazine)