Numbers 5

This chapter discusses where the unclean people would be sent, confession and restitution of sin, and a process for God to reveal whether a woman was an adulteress, even though no one was caught in the act.

Some say that "thigh" was a euphemism for a woman's reproductive organs, and falling away could mean any number of things, from failing to just closing the womb, to not being able to conceive again. This test might not have been as simple as it's written, and may take weeks to months for full proof and for the miscarriage to happen. If a woman miscarried after going through this, it would seem like divine punishment.

This was a divine test and divine punishment for adultery. This at minimum could result in divorce by the husband, and she would then go back to her father's house. Normally, the punishment for adultery was stoning.