well seeing as how im the eldest of 3 other brothers, I'd hazard a guess and say that my parents intended on having kids.
That would probably make it the other way around.
Most large families don't plan on having as many children.
They either forgo contraception, or get unlucky.
People who plan all their children tend to have just 1, or maybe 2 or 3 (usually for company for the first, or because the first is growing up).