If you are at risk for placental separation, placenta previa or preterm labor, you should not lift
at all, but if all is well, and you use common sense, you should be able to lift
whatever you feel you can handle.
The real problem comes from repetitive labor involving lifting. They have been able to relate preterm labor with very hard physical labor during pregnancy.
Hope that helps.
And here's hoping you get a BFP tomorrow, if that's what you want.