Has anyone collected colostrum during pregnancy?

I heard nipple stimulation may cause preterm labor and it’s advised not to. But lately I’ve been seeing so many people do it. All over Instagram I see posts on pregnancy pages about it. I saw one girl who posted she did it. Has anyone done it? How did you do it? When did you start pumping? How many times per day? How was your supply when you delivered? How many weeks did you deliver?