。
I'm having a baby next month.
Literal
Next-month child [object-を] give-birth-to.
生む ('to give birth to') is the transitive counterpart of 生まれる ('to be born') — The mother is the implicit subject; 子供 is the object. Without context it's slightly ambiguous whether 'give birth to' or 'have a child born,' but Japanese speakers default to 'give birth' when the speaker is female.