When the baby is born, the mother is behind her back and doesn't cry.

As far as I know, a mother-in-law is when a baby is born, with her face down and her back to the sky and not crying. Such a baby is generally called a mother-in-law in divination.

The baby born behind his mother's back is an asshole and a self-denial.

People before 12 years old and people after 12 years old are all denying themselves. That is to say, if both parents are still husband and wife after 12 years old, everything will go wrong for people born behind their mother's back.

I'm not sure if this is superstition, because no one has ever counted the fate of babies born behind their backs. I think it's biased to classify everything I don't know as superstition.