Excellent points, everyone. Great for food thought.
To clarify - I have already been in management here for several years, so I know what it takes (in our particular environment), and have been giving according effort, even after DS was born. The "promotion" I was just offered (not sure what else to call it), is to absorb 2 outside teams into my existing department. Most of the work associated with this change would be required upfront (ie: in the next few months). Which, if I stay healthy and well, should be doable.
I spoke to DH about it, and we agree I should accept the offer. I really liked a PP's point about having earned this, and not letting the fact I'm going on mat leave later change that fact. I do feel capable of the work now, and when I come back.
BTW, after my own 6-7 month mat leave, DH will take the remaining 5-6 months himself (in Canada we can split the year between the parents if desired). So once I go back, he will be full-time on the homefront for half a year, so I won't be distracted at work. I also plan to wean the girls at 6 months (like DS), to make this possible.
For sure I agree with some PPs' points that 3 kids is a major change from 1 child. Yes! BUT, my management career is a really impotant part of my self-identity, so for now I am planning to maintain it, unless I somehow later go through a total transformation of life priorities! lol
DH is an excellent and nearly equal co-parent, and often he will be the one to stay home when DS is sick. Because we know his career his less demanding than mine.
So, after thinking about it overnight, talking with DH, and reading all your excellent replies, I've decided to accept the offer, and *not* disclose the pregnancy (yet). Because I feel the risk of possibly miscarrying before 12 weeks (and having to update everyone - ick) would feel far worse to me than than the possibility that I might have some complications requiring more time off later. Yes, my boss will soon know I accepted the offer knowing I was pregnant... but in our corporate culture, it's normal not to disclose a pregnancy until 12ish weeks. So I don't think I will offend anyone by holding off.
Also, when I accept the offer, I plan to negotiate a salary review to occur in several months (not now, as I've just received a raise), in case these new team changes require so much extra effort that I feel my compensation should be adjusted accordingly.
The company is in a bit of a pinch right now, which is why they want me to accept the offer ASAP. I do like it here, so I do want to help out. And I do feel I *should* be capable to do so, even with my HT complications.
Of course, if my pregnancy becomes at risk in any way, I will tell my boss immediately and take whatever time off I need. I love the company, but not enough to put my much-desired baby daughter(s) in jeopardy!! lol
I'll update this thread again once I've officially given my acceptance to my boss.
Thanks again ladies for your thoughtful and insightful opinions.
GZ