Twitter’s monthly user base slipped 9 million year-over-year, according to the company’s fiscal fourth-quarter results, which were released Thursday.

The San Francisco-based firm’s monthly active users during the quarter were 321 million, compared to 330 million in the prior year’s quarter. Monthly users also fell 5 million from the firm’s fiscal third quarter.

After the fiscal first quarter of 2019, Twitter will stop reporting its number of monthly active users in its quarterly results. Instead, Twitter will use monetizable daily active users (mDAU) as its "audience and engagement metric," the company explained, in a statement.

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Twitter attributed the decline to sending fewer email notifications, moving away from its SMS service with phone carriers and working to cut down malicious accounts and focusing on the "health" of conversations on its service. It said abuse reports from people who interacted with their harasser declined 16 percent from a year ago, though it did not give overall numbers.

Changes the firm made to comply with the General Data Protection Regulation (GDPR) in Europe had a lesser impact, according to Twitter. The privacy law went into effect last year.

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Twitter also disclosed its daily user base count for the first time, putting the figure at 126 million, up 9 percent from a year earlier. These are users who see ads on the platform and log in at least once a day.

Twitter posted fourth-quarter earnings of $255 million, or 33 cents per share, in the October-December quarter. That is up from $91 million, or 12 cents per share, a year earlier.

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Revenue grew 24 percent to $909 million.

Shares fell sharply on Thursday, falling 9.8 percent to close at $30.80.

Fox News’ Christopher Carbone and the Associated Press contributed to this article. Follow James Rogers on Twitter @jamesjrogers