As the baby formula crisis worsens, it's also magnifying disparities in the U.S.

The mothers Tess Frear works with were already struggling. Most of them are single parents, typically from economically disadvantaged families. Sometimes they're escaping domestic violence; sometimes they're as young as 15.

For these new mothers, it was hard enough just trying to get basics such as diapers or clothing. Then came the baby formula shortage.

"There's definitely desperation," said Frear, executive director of the baby supply bank Helping Mamas in Knoxville, Tenn. "These mamas are just scared, you know. What are they going to do?"

More than three months since Abbott Nutrition issued a voluntary recall of powder formula manufactured at a Michigan production plant, further stressing pandemic-related strains in the supply chain, that desperation has become more acute. One month ago, the average out-of-stock rate nationwide was about 40%, according to the retail analytics company Datasembly. For the week ending May 28, that rate had surged to 73.6%.