Knowing your worth (professionally-USA)

Question for professionals, legal sector, paralegals would be great.

I am a paralegal, if that matters. Took me a few firms to find the right fit, and I’m pretty sure this firm is it. I have been here 3+ years and with a lot in my personal life going on, my boss has been supportive through it all. In the work place, attorneys come to me for advice, and not my more senior coworker. They invite me to meetings with clients and outside counsel.

So what’s the problem? My old coworker who I got a job barely made it past his probation period got fired for drinking on the job. I reached out to him once I heard through the grapevine what happened, and said I don’t judge him and if he needs help please don’t hesitate to reach out. I’ve been through a lot of ish in my life so sometimes someone who has an issue needs help and not feel judged...

Anyways back to my point, he tells me he got another offer at another firm, sends me offer letter, it’s for $20k more than I’m making!!

I always read about how women are paid less than men and a big component is not negotiating when they should. My review is in December, how do I approach the subject of I know I’m worth way more than your paying me?! (Side note, I’m going on maternity leave in January. 6-8 weeks at 60%pay then unpaid 4-6 weeks)