opinions please

Eve • 👦🏼💙
I had a miscarriage in November and was due in May. I wanted to get something to remember my baby by. I obviously will never forget but I wanted to get a ring or something in memory of my baby. I've narrowed it down to a pandora birthstone ring. I don't know what month to get however. I miscarried in November, went back to the hospital on December where I passed the placenta and was told that I had 'officially' miscarried that day and I was due in May. It was a missed miscarriage so although I was 13 weeks in the November my baby didn't actually make it past 4 weeks or so. 
Do I go with the November birthstone when the miscarriage started as if that was when my baby was 'born', the December when I passed the placenta and officially miscarried or may when I was due? Just wondering what other people think or would do/have done. 
Thank you in advance xx