postnatal; after birth; since birth
Used to describe the period after birth, often with time expressions like 生後3か月 (three months after birth). Can function as a noun or adverbially.
I have a six-month-old baby.
I received a vaccination right after birth.
Babies who are three months old start smiling more.
They were discharged from the hospital ten days after birth.
The kitten was taken in shortly after it was born.
Sometimes vaccinations are given right after birth.
生後 describes the baby's age since birth, while 産後 describes the mother's recovery period after giving birth.
出生 refers to the event of being born (as in birth records or statistics), while 生後 refers to the elapsed time since that birth.
Compound of 生 (life, birth) and 後 (after). The reading せいご is the standard Sino-Japanese on'yomi combination.