GREENSBORO, N.C. — Walgreen and CVS Caremark, the biggest U.S. drugstore chains, are betting they can generate sales by answering a question few men want to ask: whether or not they’re firing blanks.

In April, Walgreen’s 7,800 U.S. stores plan to start selling a fertility test that determines if a man is producing enough sperm to get a woman pregnant. Walgreen and CVS have already started selling SpermCheck Fertility online.

The blue-and-gold box, which features a smiling couple holding a newborn, will join more than two dozen varieties of female fertility tests in Walgreen stores. SpermCheck’s owner and distributor, closely held ContraVac Inc., is banking on women dropping an extra $40 for the test when they buy ovulation and pregnancy kits for themselves.

“In our society, the woman carries the burden of trying to determine the issues surrounding infertility,” said Ray Lopez, ContraVac’s chief executive officer. “Men don’t say, ‘Let me go to the urologist and give a semen sample.’”

That reluctance has created a $440 million-a-year market for male fertility tests in the U.S., Lopez says.

Every year, about 7.3 million women in the United States have trouble with pregnancies, according to the Atlanta-based Centers for Disease Control. Many women, assuming they are to blame, visit gynecologists. They are “poked and prodded” and sent home while few husbands want to consider that they’re possibly at fault, according to Barbara Collura, executive director of Resolve: the National Infertility Association in McLean, Va.

SpermCheck joins “dozens of tests” Deerfield, Ill.- based Walgreen sells to consumers “seeking less expensive and more convenient alternatives to various forms of health testing,” Jim Cohn, a company spokesman, said in an email. It helps “customers take a proactive role in their health and wellness,” said Carolyn Castel, a spokeswoman for CVS, based in Woonsocket, R.I.

Revenue at Walgreen, hurt by the loss of a contract with employee prescriptions manager Express Scripts Inc., will be little changed at $72.3 billion in the fiscal year through August, according to analysts surveyed by Bloomberg. CVS will increase sales by 11 percent to $119.5 billion this year, according to analysts.

A private-equity investor in Greensboro, N.C., Lopez joined ContraVac as a director in 2004 when he and other investors took a stake in the biotech startup. The majority owner is John Herr, the test’s inventor and director of the University of Virginia’s Center for Research in Contraceptive and Reproductive Health in Charlottesville. SpermCheck received Food and Drug Administration approval in 2010, almost 30 years after Herr, 63, and university colleagues started the research.

The test requires the man to combine his semen with a solution in a bottle, then place drops of the mixture on a test strip. A reddish line indicates the sperm count is normal — 20 million or more per milliliter of semen — while a negative result shows no color. Any reading below normal means men “should consult a physician about a complete fertility evaluation,” according to the test’s instructions.

“There is nothing like it on the shelf,” said Maeve Egner, president of Princeton, N.J.—based Fusion Marketing, hired by Lopez to help market SpermCheck. “It’s plugging a gap.”

It’s not necessary for men to test sperm counts at home if they’re willing to visit a doctor for a complete semen analysis, according to Larry Lipshultz, a Houston urologist and chief of the Division of Male Reproductive Medicine and Surgery at Baylor College of Medicine.

Determining the concentration of sperm in semen is one consideration in assessing male fertility, Lipshultz said. Others are the volume and sperm’s ability to swim, he said.

“If the sperm count is OK but the motility, how well they’re moving, is bad, those sperm aren’t going to fertilize well,” Lipshultz said by telephone.

He says women struggling to get pregnant should see gynecologists and their male partners should visit urologists for a semen analysis, which costs $100 at his practice.

Walgreen and CVS “recognized the need for the product and that it would bring new revenues to their stores,” said Lopez, who met with buyers from the two retailers at a family planning trade show in Orlando in August.

SpermCheck, though, may not become a blockbuster product, according to Gene Detroyer, a consultant to startup companies and an adjunct professor of entrepreneurship at the European School of Economics in New York. “Unlike pregnancy and ovulation tests that women try once a month, men may use it once,” Detroyer said.

Only two in 10 men are willing to accompany their female partners on trips to gynecologists when they’re having trouble with pregnancies, Herr said.

“Men have a greater tendency to believe in their invincibility,” the scientist said. “When it comes to reproduction, they are more concerned about the delivery vehicle than they are about what’s delivered.”