Fetching details from the dictionary...
post-natal; since birth
生後せいごすぐに授乳じゅにゅうする。
I breastfeed immediately after birth.
生後せいご間かんもない赤ちゃんあかちゃんを抱いいだいた。
I held a baby who had just been born.
生後せいご一いち年間ねんかんの成長せいちょうを記録きろくした。
I recorded the growth during the first year after birth.