Polite form of 誕生会, used when referring to someone else's birthday party or in formal contexts. The honorific お adds politeness.
See also: 誕生会
I was invited to my friend's birthday party next week.
お誕生会の準備はもうできましたか。
Are the preparations for the birthday party ready yet?
Standard polite spelling with honorific prefix お.
Formal or literary spelling using the kanji 御 for the honorific prefix. Rare in everyday writing.
Compound of honorific prefix お + 誕生会 (birthday party). 誕生会 itself is from 誕生 (birth) + 会 (gathering).