In Psalm 139:13–16, the author asks for our attention to the fact that God’s eyes reach inward to the womb, where new life is formed. Also there we are certainly (the Hebrew beginning of the verse underlines this) not hidden from God. He weaves our inner being.
Jeremiah hears the same (in Jeremiah 1:5) when he is called to be a prophet: Before I formed you in the womb I knew you, and before you were born I consecrated you; I appointed you a prophet to the nations.
13 For you formed my inward parts; you knitted me together in my mother’s womb.