Is drinking senna tea safe during pregnancy?

No. Pregnant women should not take senna tea because it can cause premature contractions and miscarrage. Lactating mothers should also avoid it to prevent it from causing a laxative effect in the baby's digestive system. Look up other effects of senna tea before you make it part of your diet at any time. Take care.
Senna. Medline plus indicates that senna is "possibly safe" during pregnancy when used briefly, in small doses. However, it considers the herb to be "possibly unsafe" in large doses or for an extended period of time. The american pregnancy association specifically advises against stimulant laxatives during pregnancy, noting that they can cause contractions in the uterus. Senna can also lead to dehydratio.