As a parent, I resent this comment.
I have two children, both were born within 10 months of deciding to have them (apparently we are pretty potent). I would say that we, as parents, understand sex as a reproductive instrument pretty well.
That's why he said the word often, rather than always. You made a decision to have children. I did the same thing. Most of my peers were the same.
However a large number of children are unplanned. Not necessarily because the parents didn't know how to prevent conception, but that they didn't want to.