SAN FRANCISCO -- Amazon.com ( AMZN) edged past Wall Street earnings estimates for the third quarter but offered a cautious outlook for the fourth quarter. Shares of Amazon plunged more than 13% in recent after-hours trading to $43.29. The stock has been pummeled in recent days over fear of a slowdown in consumer spending. The company posted a 48% increase in profit, climbing to $118 million in the third quarter, or 27 cents a share, from $80 million, or 19 cents share, a year ago. The results include a benefit of $15 million related to net foreign currency remeasurements. Analysts surveyed by Thomson Reuters had predicted earnings of 25 cents a share. Amazon's sales in the third quarter were up 31% to $4.26 billion, compared with $3.26 billion a year ago. That came at the low end of the company's guidance and fell short of Wall Street estimates of $4.28 billion. Excluding the $80 million favorable impact from year-over-year changes in foreign-exchange rates throughout the quarter, sales grew 28% compared with a year ago. For the fourth quarter, Amazon expects revenue in the range of $6 billion and $7 billion. That was shy of Wall Street estimates for $7.05 billion. "We remain relentlessly focused on delivering value to customers through lower prices, improved selection and our free shipping offers, including Amazon Prime," said Jeff Bezos, founder and CEO of Amazon.