I happened to come across this story and found it to be a very clear description of intrusive thoughts. If you've experienced them in the past or are worried about them now, you will want to read this: Dads Have Postpartum Obsessive Thoughts About Babies Just as Moms Do. Here's an excerpt:
A new Mayo Clinic study appearing in the Sept. 3  issue of the Journal of Clinical Psychology in Medical Settings shows 69% of mothers and 58% of fathers report having postpartum obsessive thoughts or worries about their new babies. The study surveyed 300 childbearing women and their partners, asking them questions about seven subjects including:
Suffocation or SIDS
Losing the infant
Unacceptable sexual thoughts
While surveys showed that fathers do obsess about these subjects, it found mothers did so more.
It also states that researchers found there was " … a big difference between having postpartum obsessive thoughts that will not lead to violence, and psychotic thoughts that may lead to the rare case of a parent harming the child. That difference is having fear of harming the child and being repulsed or afraid at the thought versus parents viewing their thoughts as realistic and rational."
I had no idea that new fathers had those thoughts as well. Obviously, they rarely mention it.
The only thing I really don't agree with is the last sentence: that it's best to simply dismiss such thoughts. There was no way in hell I could have just ignored them. They were unbelievably disturbing. Since thoughts such as those may indicate a postpartum mood disorder, it seems to me it would be better to seek a professional to find out whether you might need treatment in the form of therapy or medication.