Teas safe in pregnancy

So I read that lemongrass tea and blackberry leaf tea shouldn’t be consumed in pregnancy because they can both cause contractions. My question is, would that be an issue at 38 weeks pregnant?

Also note that they said it’s unsafe in large quantities. The tea I’m looking at has a blend of like 7 different ingredients, 2 of them being blackberry leaves and lemongrass so it’s not a straight cup of either one. And it would only be 1 cup, not even on a daily basis. Mostly asking this hypothetically because I wouldn’t drink it until asking my midwife but I’m just curious🤷🏻‍♀️