Red raspberry leaf tea has been used for a long time to help tone the uterus and help ease delivery. Many midwifes will use this tea to help ripen a cervix, though whether or not this actually does that is not known. Other uses include nausea and vomiting, for breast milk supply, diarrhea, and excessive menstruation.
In one study done, red raspberry did shown to help decrease the length of second stage. Also, those who were taking red raspberry tablets were less likely to need forceps or vacuum. On the other hand, more of these women experienced preeclampsia or hypertension during pregnancy. In either case the difference for all to these were not large.
In another study, it showed a decrease in prematurity, overdue labors, and medical intervention.
While there is not much research, it appears that red raspberry tea is safe during pregnancy.