Pregnant Serena Williams Smashing Tennis Balls In 3rd Trimester

Serena Williams is such an insane athlete, she's playing tennis while 7 months pregnant -- and will still destroy all comers!!

SW is roughly 28 weeks with child (that's the 3rd trimester btw) -- but despite her growing baby bump, the tennis superstar busted out her racket and smashed some baseline forehands this morning.

To put it in perspective, Parents.com says her baby should be the size of an eggplant right now!

We already know she won the Australian Open while that human being was cooking inside her. Question is ... how many people could she take down now?