Twitter (TWTR) provided light guidance for the fiscal first quarter of 2019 and said it expects operating expenses to increase this year, overshadowing strong top- and bottom-line results in the fiscal fourth quarter of 2018.

Shares of Twitter fell 7.14% to $31.72 each as of 7:15 a.m. ET. The stock was up about 18.9% in 2019 as of market close Wednesday.

The San Francisco, California-based social media company posted fourth-quarter revenue of $908.8 million, ahead of consensus estimates of $867.1 million, according to Bloomberg data. Earnings, excluding some items, were 31 cents per share, exceeding consensus estimates of 25 cents per share.

The social media company said it expects to see revenue of between $715 million and $775 million in the fiscal first quarter of 2019, with the midpoint of that range coming below the average analyst estimate of $766.1 million. The company expects its GAAP and cash operating expenses will be up about 20% in 2019 “as we support our existing priorities of health, conversation, revenue product and sales, and platform,” Twitter said.

The San Francisco, California-based social media company said monthly active users fell to 321 million in the fourth quarter from 326 million in the third quarter. Consensus expectations were for a decline to 323.8 million, according to Bloomberg data. In the year-ago quarter, monthly active users had totaled 330 million.

The social media company said that it will no longer break out monthly active users after the first quarter of 2019. The metric had been a key measure of the platform’s user engagement.

Instead, Twitter said it will report monetizable daily active users to show the size of its audience and engagement going forward. These are users that log in and access Twitter on any given day through twitter.com or on Twitter applications that are able to show advertisements. The company said average monetizable daily active users were 126 million in the fourth quarter, up 9% year-over-year.

“We believe that monetizable DAU (mDAU), and its related growth, are the best ways to measure our success,” the company said in a statement.

“This change in disclosure does not impact the objectives which bring advertisers to Twitter or the information to which they have access today,” the company added. “Advertisers come to Twitter because we have one of the most valuable audiences when they are most receptive, and we generate a high return on investment against their campaign objectives whether they are launching a new product or connecting with what's happening on Twitter.”

Part of Twitter’s monthly active user decline is attributable to the company’s ongoing user clean-up efforts. Twitter announced in mid-2018 that it was wiping millions of fake and suspicious accounts off its platform as it aimed to clean up the site and improve the user experience. The purge in part led the company to miss expectations on monthly active users in the fiscal second and third quarters of 2018.

“Our focus on improving the health of the public conversation on Twitter delivered promising results in 2018, with a 16% year-over-year decrease in abuse reports from people who had an interaction with their alleged abuser on Twitter, and enforcement on reported content that was 3X more effective,” the company said in a statement announcing fourth-quarter results.

Twitter’s 9 million-user drop in monthly active users last quarter had been the company’s steepest quarterly decline. However, investors had largely shrugged off the shortcoming last quarter amid otherwise strong top-and bottom-line results and the company’s previously stated account clean-up efforts. JPMorgan analysts wrote in a note Wednesday that Twitter’s user health progress “should drive benefits to usage and advertising revenue long-term.”

Many analysts carried a bullish outlook for Twitter ahead of Thursday’s results. Twitter’s stock earned a double upgrade to Buy from Underperform by analysts at Bank of America Merrill Lynch on January 10, with the analysts citing better user penetration and improving metrics in the key 18-29 young adult demographic.

Twitter had a high bar to meet in its latest quarterly report given strong recent results from peer Internet companies. Facebook (FB) and Snap (SNAP) cut through concerns of data privacy and declining engagement, respectively, to deliver better-than-expected quarterly results. And both Facebook and Google-parent Alphabet (GOOG, GOOGL) reported strength in advertising sales, especially domestically, where Twitter has high ad revenue exposure. Twitter’s fourth-quarter U.S. revenue totaled $506 million, a 24% increase, while international revenue was $403 million, a 27% increase on a constant-currency basis.

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Emily McCormick is a reporter for Yahoo Finance. Follow her on Twitter: @emily_mcck

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