INNERSPACE

I'm pretty sure this is the movie I'm thinking of. Innerspace was made in 1987, it got an Oscar and some awards for visual effects.

The reason I'm posting this is I remembered something.

When I was about 6 or 7 I was convinced you could get pregnant from sharing spit, or kissing someone. So I would get really paranoid about when people would kiss me on the cheek and I would always go to the bathroom after to see if my tummy had grown. It was pretty crazy. The reason I thought this was because I saw a movie where there was a small man in a submarine in a guys body, and when the guy kissed his girlfriend the man in the submarine went into her and found out she was pregnant and then returned to the guys body. So after seeing that, I was convinced that kissing was what immediately got you pregnant. And I'm pretty sure it was this movie. The video of the trailer is below (or after the link).