There have been a lot of stories like this in the news over the past couple of years, for example:

https://www.telegraph.co.uk/news/9193014/British-man-fathere...

https://edition.cnn.com/2016/09/13/health/fertility-doctor-i...

http://www.dailymail.co.uk/news/article-4504648/Head-Dutch-c...

http://www.rebelcircus.com/blog/fertility-doctor-used-sperm-...

https://news.sky.com/story/dna-of-fertility-clinic-doctor-ac...

Shocking how frequent this behaviour appears to be.

I just heard a This American Life about something similar[1].

[1] https://www.thisamericanlife.org/289/go-ask-your-father/act-...

That was in the 80s. These days one would think fertility doctors would know better than getting themselves on the hook for child support.

Well, that is bizarre and somewhat horrific

How exactly did they get doctors DNA for comparison?

Perhaps he also tried to check his ancestry, and thus his DNA was on file.

Yeah, but you'd think he'd realize that something like this would happen (assuming that this wasn't an isolated incident and like similar cases he'd been using his own sperm routinely).

People who have committed crimes make mistakes all of the time.