I'm in the same boat, I'm highly responsible, always have the the smart, older child and now I'm pregnant. I haven't told my mother yet, and I'm not sure when to tell her, I've lived on my own for 3 years now, I'm just afraid she'll be disappointed, not to mention telling my grandmother, HA.
I am 5+6 and told my mum and was scared as in April she was saying how shes 40 and not a grandma and im 20 but i was pleasently surprised of how she reacted and shes a rock for me now :)
I have the same thing I'm my mothers only chance to re produce and when I told her it took her a while she live across the country and she actually really sad she cannot be here to watch and help me ") I'm 5W1D
She'll understand. Just call her and tell her. She shouldn't be ashamed to be a grandmother at 40 my mom wasn't a grandmother until she was 43. It's not like your 16 and pregnant. Good luck.