McDonald’s Corp. (NYSE: MCD), the world's biggest fast-food chain, is expected to report virtually flat first-quarter results as smaller profit margins slightly offset an upturn in global same-store sales in the latter part of the three-month period. 

The Oak Brook, Ill., company, which has 34,480 restaurants worldwide, is expected to report Friday that it had net income of $1.27 billion, or $1.27 per share, compared with $1.27 billion, or $1.23 per share, according to an analyst survey by Thomson Reuters. Revenue is expected to rise slightly to $6.59 billion, up from $6.55 billion a year earlier.

Barclays estimates that, compared to unusually strong sales in the first quarter of 2012 because of unusually warm weather, sales in the first quarter of 2013 will be down about 2 percent. McDonald's global same-store sales surged in the first quarter of last year by 7.3 percent, while comparable sales in that quarter were down 1.9 percent and 1.5 percent in January and February, respectively.

Trefis said in a note that McDonald's same-store sales in January and February of this year were down 1.9 percent and 1.5 percent, respectively. Same-store sales are a key retail metric because it only measures the performance of outlets that have been open for a year or more and excludes the effect of currency fluctuations.

Besides the comparatively weaker same-store sales in the recently completed quarter, McDonald's first-quarter results will reflect smaller profit margins, said Trefis. The smaller margins reflect the company's decision to respond to declining traffic by stressing its Value Menu items, which carry lower margins.

UBS analyst David Palmer sees the same story playing out in the first quarter.

"The early success of 2013 has been McDonald's ability to stabilize its U.S. same-store sales growth and significantly outperform the industry with the help of value," Palmer said last month in a note. "Additionally, a unified national value message has created a base for future trade-up as premium innovation hits in the second quarter. We note that McDonald's outperformed U.S. fast food peers by 2.5-3 percentage points in February."

Overall, however, Palmer expects the recently completed quarter to "be a relatively low growth quarter."