From everything I've read, it comes in during the last month for most women. However, I've been leaking heavily since the 4th month. It's still coming in strong, and I'm due in 3 days! I guess my body was just set on bf since the beginning!
Edited: I've been leaking since the 4th month, but didn't have dark yellow leaking (what I guess is colostrum) until the 6th month.
With my first I started leaking colostrum at about 16 weeks. With my 2nd, my first was still nursing and she told me it came in at about 28 weeks. She came off the breast saying "Mmmm yummy!" And she gained about 5 pounds that first month of it! LOL I'm 19 weeks now with my 2nd still nursing and it's still the tiniest bit of milk.
I noticed more early in this pregnancy but I haven't had any in a while. I can express a drop but that's it. I remember having to really squeeze with my other kids too... I don't often leak in pregnancy.. but rest assure I've never lacked milk after the babies came out.
I had HUGE oversupply with the girls and this time I'm hoping for the same since I'm going to start pumping for my 2 year old again.
With my 1st pregnancy I noticed it around 7 months, and at about 5 with my second. But with this pregnancy, I've noticed that the little bit of milk that's left for my toddler is getting a yellowish tinge to it lately. Nursing has also been a lot less painful and I'm wondering if there's a connection.
Usually your body is ready to make colostrum by 21-24 weeks. Some people leak, some never leak. The place you can easily check is after a hot shower try hand expression and you should be able to see a drop or two. It is rare a mother of a 23/24 week premature baby isn't able to provide milk when asked to in my experience.