Amazon.com Inc on Thursday forecast first-quarter sales below , even as sales for the holiday quarter hit a record and rose 20 percent.

The company's net sales increased 20% to $72.4 billion in the fourth quarter, compared with $60.5 billion in fourth quarter 2017. Excluding the $801 million unfavorable impact from year-over-year changes in foreign exchange rates throughout the quarter, net sales increased 21% compared with fourth quarter 2017.

Operating income increased to $3.8 billion in the fourth quarter, compared with operating income of $2.1 billion in fourth quarter 2017.

Net income increased to $3.0 billion in the fourth quarter, compared with net income of $1.9 billion, in fourth quarter 2017.

For the full year 2018, Amazon said its net sales increased 31% to $232.9 billion, compared with $177.9 billion in 2017. Excluding the $1.3 billion favorable impact from year-over-year changes in foreign exchange rates throughout the year, net sales increased 30% compared with 2017.

Operating income increased to $12.4 billion, compared with operating income of $4.1 billion in 2017.

Net income increased to $10.1 billion compared with net income of $3.0 billion in 2017.

“Alexa was very busy during her holiday season. Echo Dot was the best-selling item across all products on Amazon globally, and customers purchased millions more devices from the Echo family compared to last year,” said Jeff Bezos, Amazon founder and CEO. “The number of research scientists working on Alexa has more than doubled in the past year, and the results of the team’s hard work are clear. In 2018, we improved Alexa’s ability to understand requests and answer questions by more than 20% through advances in machine learning, we added billions of facts making Alexa more knowledgeable than ever, developers doubled the number of Alexa skills to over 80,000, and customers spoke to Alexa tens of billions more times in 2018 compared to 2017. We’re energized by and grateful for the response, and you can count on us to keep working hard to bring even more invention to customers.”

The company forecast net sales of between $56 billion and $60 billion for the first quarter.