Breakdown of Кстати, завтра у мамы день рождения.
мама
mom
завтра
tomorrow
день рождения
birthday
кстати
by the way
Questions & Answers about Кстати, завтра у мамы день рождения.
Why do we say у мамы день рождения instead of using the possessive and saying мамин день рождения or день рождения мамы?
Using у plus the genitive case is the most natural, idiomatic way in conversational Russian to express that someone has an upcoming event or milestone. While день рождения мамы is grammatically correct, it sounds much more formal. Мамин день рождения is also okay, but у мамы remains the most common everyday choice.
I sometimes hear native speakers treat the event as a single neuter word. Is it день рождения or день рождение?
It is strictly день рождения (literally, day of birth). The core noun is the masculine день, and рождения is just a modifying noun in the genitive case. Even though some native speakers mistakenly treat the phrase as a single neuter noun ending in -е, you should always treat день as the only part that changes case. For example, to wish someone a happy birthday, you put the first word in the instrumental case: С днём рождения!
How does the word order in this sentence affect its meaning? Could I say Кстати, завтра день рождения у мамы?
You can, but it changes the emphasis. In Russian, the most important new information usually goes at the very end of the sentence. The original sentence emphasizes the event itself: what is happening tomorrow? A birthday. If you put у мамы at the end, it emphasizes whose birthday it is: tomorrow is mom's birthday, not someone else's.
Does the transition word have other meanings besides by the way?