I'm sure most don't. But some do. I know of at least one who has written she regretted it (adopting her kids) and wished it had never happened.

It seems to me that anyone who is a parent might have regrets, but I also realize that adoptive parents who come to adoptive parenting unprepared might have regrets that one normally wouldn't see.  I honestly don't know, though. It's an interesting question, and I'd love to see some statistics on this, although I doubt they exist.

I do know that in my case, there has never been a moment's regret.  My kids are on the verge of adulthood, and living without the day-to-day parenting routine honestly frightens me.  If someone said I could do it all over again, I'd say yes in a heartbeat.

Adoptive moms are human, and as such I have to assume that some are/were ill prepared for parenting, and/or had unrealistic expectations, and/or unreasonable ideals, and/or were not adaptable to the realities of parenting, and therefore "regret" it just as any parents might.

I'm sure some do. I don't know much about the rates of adoption disruption (when an adoption is "undone") but I do know that they're higher in international adoption and foster-to-adopt in part because parents get in over their heads and aren't adequately prepared for the special needs of kids who have a challenging history.