In VI, Terra's parents basically ~love~ each other into pregnancy. It wasn't until VII when there was, like, tons of sex all over the place. Honeybee Inn, Don Corneo, Cloud+Tifa (debatable).

VIII went back to being pretty sterile, despite being a story about teenagers in love. IX has Zidane running around being ladies man, but then became a boy-meets-girl story (not criticizing). X ditto.