Well, I don't know the exact answer to all those questions.
But, if you get pregnant/injured when you are ranked, say, #40 in the world then when you come back you are allowed a certain number of tournaments you can enter at the #40 ranking even though you have fallen to, say, #120. That makes a big difference in being allowed to get into the main draw of tournaments.
If you do well and your rank goes up (from 120), that's a good thing but if, after the requisite amount of tournaments you are still below your pre-injury rank (40) then you will drop down to your ACTUAL rank and have to enter qualifying, etc. to get into the main draw.
This is what I understand but someone else might know otherwise.
If so, anyone is invited to dispute what I said. I won't get mad.
After all, I didn't look it up, I just answered off the top of my head.