“当祖母”常见的英文表达是 “become a grandmother” 或 “become a grandma”（“grandma”是“grandmother”的非正式、口语化说法）。
例如：
She is going to become a grandmother next year.（她明年就要当祖母了。）
My mother became a grandma when her first grandchild was born.（我妈妈在第一个孙辈出生时当上了祖母 。）