Amazon’s profits were hit or miss for its first couple of decades. But now, for the first time, they are starting to look consistent — with four consecutive quarters above $1 billion in profit.

On Thursday, the company reported a net income of $2.9 billion in the third quarter, surpassing analyst expectations. But the focus on profit that investors have long sought wasn’t enough to keep them happy. The company’s shares dropped more than 7 percent in aftermarket trading, after Amazon also announced that revenue in its core retail business was growing more slowly than in the past.

The company’s sales were up 29 percent to $56.6 billion, below what analysts had predicted. In Amazon’s biggest business, its online store, sales rose just 11 percent over the past year. A year ago, the pace was twice as quick.

“They are saturating the core market in the U.S. for e-commerce,” said Cooper Smith, who leads Amazon research for Gartner L2. “This is a company in transition right now,” moving from a focus on acquiring more customers to getting more growth from people who already shop the site.