<p>My daughter hasn’t had a teacher who was pregnant- but I do know what you are talking about.
I expect that those teachers who worked until their last month were committed professional teachers, who realized that their classroom had a huge impact on these kids, and they didn’t want to leave them in the hands of “subs”, until they absolutely had to.
As opposed to my daughters 5th grade teacher, who left the classroom a few weeks after the start of the school year, to spend time with her mother who was ill ( teacher was in her late 50’s, so I expect mom was equally advanced in age 
)
Thats fine, we all have our priorities, except she wouldn’t take a permanent leave, so that another teacher could be hired, and subs rotated through her classroom until her mother passed away Five years later.</p>
<p>Many careers actually demand you work as much as possible before taking maternity leave. I had to go on bedrest & lost my job over it because I was gone longer than six weeks, I also remember my mother in law telling me about a woman who drove herself to the hospital when she was in labor ( implying I should be doing the same thing and not be bothering the father), and other women who had 6 weeks off max, so they waited until as long as possible to leave work before the birth in order to maximize time with the baby.</p>