3D Systems (DDD -1.43%) is set to report its final first-quarter earnings on May 6 before the market opens. Unfortunately, investors already know that the results will come in well below expectations, as the company released the preliminary results last week. However, there are still many unanswered questions about the quarter and whether the long-term investment thesis remains intact.

The following three areas will help investors gain further insight into how 3D Systems' underlying business is performing.

1. North America
During 3D Systems' most recent fourth quarter, the company's North American operating segment performed poorly compared to other geographies, and weighed heavily on the company's organic growth rate -- the rate of annual revenue growth excluding acquisitions over the past year. All told, 3D Systems' fourth-quarter organic growth rate collapsed to 7%, down from 34% the year prior.

3D Systems attributed the underperformance to a major sales shift as the company moved away from selling midrange jetting 3D printers to almost exclusively selling high-end production printers. This shift in focus ultimately resulted in weak overall unit growth for its jetting printers, and hurt the entire geography's operating performance.

Although 3D Systems has begun taking actions to remedy the situation, and management noted during the preliminary earnings call that it's difficult to gauge any improvement in light of the company's weak first-quarter results, investors should still monitor how the improvement is progressing. After all, 3D Systems' North American segment is large enough to influence the company's overall performance, and shouldn't be dismissed.

2. The capital spending environment
One of the more troubling aspects to 3D Systems' preliminary results was that its major customers have been delaying future purchases of 3D printers, materials, and services for a number of reasons, including the continued strength of the U.S. dollar and the aftermath of low oil prices.

During the preliminary earnings conference call, it came to light that 3D Systems' major customers across a variety of industries were reevaluating their capital spending plans as they assess the impacts of these macroeconomic headwinds on their businesses.

This is a dangerous dynamic for 3D Systems, because in a weak capital spending environment demand for the company's offerings could quickly dissipate as customers postpone their future purchases until the macroeconomic landscape improves. If enough of 3D Systems' customers walk this line, it could significantly impact the company's future operating performance.

3. Operating leverage
On numerous occasions over the last year, 3D Systems has promised that its operating leverage, which management defines as revenue growth outpacing non-GAAP operating expenses, will begin to return in the second half of this year, and be fully restored by 2016. In theory, improved operating leverage should trickle down to the bottom line in the form of improved earnings.

At this time, it's unclear whether this plan remains on track -- management doesn't expect to report any organic growth in the first quarter. If 3D Systems' can't meet this goal, it weakens the long-term investment thesis, which is partially reliant on the promise of future earnings growth. 

All eyes on Wednesday
When 3D Systems reports earnings on Wednesday, investors should focus on how the underlying business has been performing, rather than how other investors react to the news.

During the conference call, listen for how 3D Systems' North American segment fared, for clues about the current state of the capital spending environment, and for whether the company's operating leverage plan is still on track.