It's very bad for your back and pelvis! All of your ligaments soften and heavy lifting can cause injuries a lot easier than when you're not PG.

If I had my time again I'd certainly not be lifting slabs again. I used to work in a bottle shop and during my first PG kept it up because I was used to it. I noticed that lifting at the time wasn't so bad but there would be an aching about 10 mins later. I was doing this untill I finished working at 32 weeks PG.

Now I have constant pain and sciatica and my 2nd and subsequent PG's were hell. I know that SPD and pelvic instability can happen to anyone but I believe that lifting as much as I did contributed to it.

End lecture

Honestly it's not worth it so let someone else do it for you if you can.