It is true. Here is an introductory popular article to start reading about it. http://thechart.blogs.cnn.com/2011/11/18/baby-in-parents-bed...

Keep in mind how many mothers there are, and how many of those rare incidents had extenuating circumstances (substances, atypical neurology in the mother.) Keep in mind how easy and cheap it is today to extend the width of a bed with an attachment.

I know that the downvotes come from people who think of mothers sleeping with their children as poor trash—it’s a seriously outdated view that hurts the child.