Facebook (NASDAQ:FB) reports fourth-quarter results Wednesday after market close. With shares up 42% in the past 12 months, the expectations for the social network are high. Can Zuckerberg and Co. deliver? Here are some of the most important metrics to check on when the company shares the results from its latest quarter.

The market expects big year-over-year growth in revenue from Facebook -- not just this quarter, but also for years to come. These expectations are evident by looking at the company's rosy valuation. Facebook trades at 19.3 times sales and 73.6 times earnings. For comparison, Google trades at a much more down-to-earth 5.4 times sales and 27 times earnings. For Facebook to live up to such optimistic expectations, it will have to grow its business at double-digit rates over the long haul.

But what growth, exactly, should investors expect from Facebook in Q4? Analysts, on average, expect Facebook to report revenue of $3.8 billion, up 46.1% from the year-ago quarter. While this number is big, it's down considerably from the 72% year-over-year revenue growth Facebook reported in the first quarter of the year.

Analysts' expectations for Q4 revenue are reasonable in light of the continued trend of decelerating year-over-year revenue growth rates for Facebook. This level or revenue growth would mark the company's third quarter in a row of decelerating year-over-year revenue growth rates. In Q3, Facebook's revenue grew 59% from the year-ago quarter.

As Facebook's social network matures, investors are wondering how long the company can hold up its impressive engagement metrics. So far, engagement on Facebook's platform has improved every single quarter since the company went public. But there will come a day when engagement on Facebook's platform can no longer improve. Could this be the quarter that engagement finally levels off?

To look at how engaged Facebook's members are on its platform, divide daily active users by monthly active users. In Q3, engagement hit an all-time high of 64%, up from 62% in Q2. Investors should look for an engagement rate of 64% or higher in Q4. A decline in Facebook's engagement rate could be a red flag, especially in light of how dependent Facebook's revenue is on its social network platform.

Facebook CEO Mark Zuckerberg (right) in Facebook conference room. Image source: Facebook.

Other items to watch
Look for user growth. In Q3, Facebook reported 864 million daily active users and 1.35 billion monthly active users, up 19% and 14% from the year-ago period, respectively. Expect more year-over-year growth in both daily and monthly active users.

With the company's history of reporting higher EPS than expected, it would be great to see Facebook beat expectations. Analysts expect Facebook to report EPS of $0.48, up from $0.31 in the year-ago quarter.

However the market reacts to Facebook's report, investors should keep in mind that this is just one quarter. While it's possible that information provided in a single quarter could be enough to support a buy or sell decision, investors should remember to zoom out and keep in mind the broader story for Facebook before they make any decisions about Facebook stock.

Facebook reports fourth-quarter results after market close. A copy of the earnings release will be available here. Investors can tune into a live earnings call at 5:00 p.m. ET here. Check back at The Motley Fool for post-earnings coverage.