Amazon's fourth-quarter results beat estimates, but weak guidance and general concerns about slowing growth and heavier investments in 2019 dragged the stock down in after hours trading.

Here are the most important numbers:

EPS: $6.04 vs. $5.68 estimated, according to Refinitiv

$6.04 vs. $5.68 estimated, according to Refinitiv Revenue: $72.4 billion vs. $71.9 billion estimated, according to Refinitiv

$72.4 billion vs. $71.9 billion estimated, according to Refinitiv AWS: $7.43 billion vs. $7.3 billion estimated, according to Refinitiv

Amazon shares dropped more than 5 percent in extended trading after the company warned of increased spending this year, following a relatively slow investment period in 2018. Amazon CFO Brian Olsavsky noted during the call with analysts that the company had significantly scaled back investments last year, across hiring and capital expenditures — and that spending is now likely to pick up.

"I would expect investments to increase relative to 2018," Olsavsky said.

The better-than-expected fourth-quarter results, backed by strong holiday sales, comes as investors fret about decelerating growth following two straight quarters of disappointing revenue. Sales climbed 19.7 percent in the latest quarter, which was faster than the 18.8 percent expected, but still the slowest since the first quarter of 2015.

This was the first time Amazon provided a year-over-year number on Whole Foods, a slower growing business. That likely contributed to the pullback in North American expansion, with the growth rate dropping to 18 percent from 42 percent in the year-ago period. Revenue at whole Foods increased about 6 percent from a year earlier.