How exactly are toxoplasims / toxoplasmosis spread ?

I know by changing your cats litter but how contagious is it ? 
I have never changed our cats litter until now , i'm 33 weeks pregnant and 
I just scoop out the dry poop with the scooper , is this bad ? 
I do it because since our cat is an inside cat we don't want the house to smell . I do spray air freshener but I occasionally scoop out the poop will my baby be okay ? I'm scared of it affecting my baby