I'll expand on the tradition. It apparently came about as couples did not have sex before marriage and birth control was not really around or was not readily available or reliable. So if you were successful or your body was ready, you got pregnant on your wedding night or usually the next month, the eternity ring was to celebrate the fact the a baby meant you were together for eternity symbolising ever lasting love or if no baby, you made it to one year of marriage and again symbolising eternity

All a bit of fun really.
Which puritanical society was it where noone was having sex before marriage? Not ours surely? People have been having sex before marriage for eons...they just didn't talk about it! There were a hell of a lot of very healthy full term looking prem babies though!