Your children may resent you, but tbh, I've found that, that is more down to personality than situation.
It's all down to your DH stepping up. Only you know how likely that is.
Does he realise what a Newborn's Care entails?
Don't you get maternity Leave? How would you manage if you were to have a C-Section and complications and couldn't return to work as quick as you hoped? What if your child had disabilities/poor health, how would your DH manage?
Is he Caring towards you and does he part run the household now?
If he doesn't step up, your life could come crashing down. That's the real issue.
Your DH might not like it, but I don't think that you should wait until you are pregnant to give your ex the heads-up. Your Girls will have mixed emotions.
""It's 2018, for goodness' sake.""
That doesn't change what we expect from our Mother's. Some of it is unfair, when compared to what we expect from Fathers. But the relationship with our Mother's, hurts more, when it goes wrong.
For Girls, it often comes out when they have their First child, as well, as the Teen years.
It would be the possibility of the DH not coping and the OP having to change plans, that would worry me. other than that, the OP has treated all of her children equally, work has come first.