Amazon.com Inc. AMZN 2.49% is scheduled to release third-quarter earnings after the market closes Thursday. Here’s what you need to know:

EARNINGS FORECAST: Analysts polled by FactSet on average expect Amazon to earn $4.59 a share, compared with $5.75 a share a year ago. The company forecast operating income of $2.1 billion to $3.1 billion, compared with $3.7 billion a year ago.

REVENUE FORECAST: Analysts on average project quarterly revenue of $68.8 billion, compared with $56.6 billion a year ago. Amazon said it expects sales of $66 billion to $70 billion for the quarter ended Sept. 30.

WHAT TO WATCH:

HIGHER COSTS: Analysts expect an increase in shipping costs to weigh on Amazon’s profitability. The company’s streak of record profits ended in the second quarter after world-wide shipping costs jumped 36%, to $8.13 billion, from an average of about 20% in previous quarters.

Amazon is pouring money into making one-day shipping available for more than 100 million items on its website, spending more than $800 million during the second quarter toward the initiative. Investors will look for guidance on how costs could affect profit during the final three months of the year, which is typically a high-sales period because of the holiday shopping season. Analysts on average expect costs to be offset by revenue growth of roughly 21.5% compared with a year ago. Revenue in the second quarter grew 20% following a 17% increase in the first quarter.

AWS GROWTH: Investors will look for growth at Amazon’s cloud business to speed up after a slowdown in the second quarter. Sales at Amazon Web Services climbed 37% in the three months ended June 30 compared with the year-earlier period, after topping 40% in previous quarters. Analysts on average predict AWS growth in the third quarter to stay below 40%. Amazon counts on high profit from AWS, as well as the company’s expanding advertising division, to lift overall margins as it accumulates more costs within its core retail business.

Garments made in Bangladeshi factories that major retailers have banned as unsafe are finding their way onto Amazon's site for sale in the U.S. WSJ investigates Amazon's apparel supply chains and the impact of its marketplace on garment factory workers. Photo: Karan Deep Singh for The Wall Street Journal

REGULATION AND TARIFFS: Amazon has faced scrutiny by regulators in the U.S. and abroad over its marketplace, which has been found to favor its own products over that of its third-party merchants and sell banned items and products made in dangerous factories. The European Union is investigating whether Amazon has a competitive advantage through the data it gathers on its website, while in the U.S., the Federal Trade Commission is probing if Amazon’s web of businesses, taken together, have become too powerful. “We are monitoring regulatory concerns closely as we consider it the largest risk to the stock today,” D.A. Davidson analyst Tom Forte said in a note.

Additionally, Amazon’s reliance on products sourced from China is of increased concern to investors because of a prolonged trade war between the U.S. and China. Analysts say the trade war could have a negative impact on future retail sales.

Write to Sebastian Herrera at Sebastian.Herrera@wsj.com