家母

家母 is a humble (谦称) form used only when speaking about your own mother to someone outside the family. The pattern 家 + kinship term works for 家父 (my father), 家兄 (my elder brother), 家姐 (my elder sister). Use the matching honorific 令 + term (令堂 'your mother', 令尊 'your father') to refer respectfully to the listener's family. In casual speech, just say 我妈.

Never use 家母 for someone else's mother - it sounds nonsensical at best and rude at worst. And do not stack 我 in front (我家母 is wrong); the 家 already encodes 'my'.