My two cents worth!

Don't know...
If Kay couldn't even take the children to New England, to her parents, how could she get away by herself anywhere else — in Nevada (or surrounding areas)

I reckon, the only time:
she would have been out of the compound was for her medical appointments and then the only time she would have been not under the watchful eye of the buttonmen was when she was inside the consulting rooms just her Gynaecologist and her

I also reckon, she was needling Mike to flip She only threw the spiteful abortion at Michael after he mentioned miscarriage
Bang! live abortion Grenade — son! son! son! — thrown under Michael, to hit him where she knew would hurt him the most

1. It wasn't a miscarriage -- it was an abortion. An abortion Michael. Just like our marriage is an abortion.
2. I didn't want your son Michael -- I wouldn't bring another one of you sons into this world.
3. It was an abortion Michael. It was a son Michael, a son and I had it killed

I reckon:
1. the only opportunity was the family doctor who wouldn't dare perform an abortion on Michael Corleone's wife
2. the mystery is abortion or miscarriage?
3. the bigger mystery is Michael just accepting it
4. No mystery is we are still debating half a century on

we'd discussed in various threads including Kay's abortion — for and against... abortion or miscarriage?
The variety of the posts shows just how much nuance is contained in this absolutely beautiful cinema Let's keep them coming!