there were tons and tons of spirits waiting in heaven to receive a physical body and that as sealed members of the church, it was our sacred responsibility to bear as many children as "possible" (I put that in quotes because what possible means gets interpreted all kinds of way) to give them the chance to receive a body, be born in the covenant and raised in the true Church of Jesus Christ on earth.

I don't know how heavy that teaching was (like if it was a sin to not do it, to use birth control was a sin, or all leaders were counselled to tell all members to not stop having kids if it was brought up, etc.) but the teaching of being selfish for not having lots and lots of kids I remember was still around in the 80's when I was a teen.

Whether or not that's still an officially endorsed teaching (the recommendation of the Church) I don't know.