I found out when I was in my early 30's that my mom hadn't only had 4 kids, but actually 6 but gave 2 up for adoption before I was born. Also, i was the last baby she had with some rando before she married my stepdad and she had intended to give me up for adoption, as well.
Silver lining? One of the babies she gave up contacted her a few years after I learned about this and now I have an awesome new brother!