A baby formula display shelf is seen at a Walmart grocery store in Orlando. Stores across the United States have struggled to stock enough baby formula, causing some chains to limit customer purchases.

There appears to be no end in sight to America's baby formula shortage, according to the most recent data from a retail tracking group.

The share of baby formula out of stock across the U.S. hit 40 percent on April 24, according to Datasembly. That's up from 29 percent in March.