One's biological (birth) mother — used to distinguish from an adoptive or stepmother.
彼女は実母に育てられたが、養母にも感謝している。
She was raised by her birth mother but is also grateful to her foster mother.
実母の体調が悪く、手伝いに帰省する予定だ。
Her birth mother is unwell, so she plans to go home to help.
戸籍には実母の名前が記載されている。
The birth mother's name is listed on the family register.