Sales of the high-profit GMC Sierra pickup were up 13% in the first quarter. Strong results for high-margin products could boost GM's profits despite flat overall sales numbers. Image source: General Motors.

Detroit's earnings parade kicks off before the bell on Thursday April 21, when General Motors (NYSE:GM) reports its first-quarter 2016 earnings.

Here's a look at what to expect, and what to watch for.

What Wall Street expects: Analysts polled by Thomson Reuters expect GM to report earnings of $1.01 per share for the first quarter, up from $0.86 a year ago. On average, they expect revenue of $35.41 billion, down slightly from a year ago. 

How GM performed in the first quarter: GM sold 2.36 million vehicles in the first quarter. That was down 2.5% from a year ago, a drop that GM attributed to "continued challenging conditions in parts of South America and Asia and the softening of the mini-commercial vehicle market in China." 

One of GM's Chinese joint ventures, Wuling, has been hit hard by the drop in small commercial vehicle sales. But its primary venture (Shanghai GM) saw good growth, leaving GM and its joint-venture partners with a 0.2% year-over-year sales gain for the quarter. Strong sales of SUVs and upscale models should help boost profits over the year-ago quarter despite the roughly flat sales result. 

In North America, sales were up 1.2% in the quarter, led by a strong 7% increase in retail deliveries in the United States. The overall increase was limited by GM's choice to reduce its sales to rental-car fleets, traditionally a low-margin business. While GM's overall growth in the important U.S. market trailed most rivals', GM CEO Mary Barra has argued that the lower overall sales volumes will yield higher profit margins.

In Europe, GM's Opel subsidiary was able to gain ground in a good market. Its 8.4% first-quarter sales gain outpaced the overall market's 5% growth. GM has lost money in Europe for years, but it has predicted a roughly breakeven result for 2016.

All of that should translate into modest profit gains in North America (if Barra's theory pans out) and in China, and potentially good growth in Europe -- offset to some extent by ongoing weakness in South American and other parts of Asia.

Key future investments: Like rivals Ford, Toyota, and Volkswagen, GM is making a big effort to show that it will be a major player as technological advances transform the industry. GM made a $500 million investment in ride-hailing service Lyft in January, and announced last month that it will acquire San Francisco self-driving start-up Cruise Automation.  

Meanwhile, GM's upcoming electric Chevy Bolt is already in pre-production, and the company is known to be preparing Cadillac models with vehicle-to-vehicle communications and some self-driving functionality. We'll look for updates on all of these fronts during GM's earnings presentation.

GM Financial: GM's captive-financing unit is smaller than those of rivals like Ford, and it has substantial exposure to subprime buyers and to longer-term loans (which have higher default rates). But it has been growing: GM has said that 2016 will be the year in which the captive-financing unit becomes a significant profit center. We'll be looking closely at its first-quarter results.

The bottom line: Expect GM's per-share earnings to come in a bit ahead of Wall Street's $1.01 estimate, with revenue roughly flat versus a year ago. If Barra's theory pans out, we can also expect GM's EBIT-adjusted margin in the all-important North America region to come in well ahead of last year's 8.8% result.