LONDON — In the past decade, billions of dollars have been spent trying to save the lives of mothers in developing countries using strategies — usually inexpensive drugs — deemed essential by the U.N. health agency.

Yet two large analyses of maternal health programs— including one conducted by the U.N. itself — report that the efforts appeared almost useless, raising troubling questions about why all that money was spent.

While critics are calling for the pricey global initiatives to be significantly overhauled, the programs are still being implemented despite little proof they work. The practices mainly involve things like ensuring women giving birth get cheap drugs such as magnesium sulphate to treat labor complications or pre-emptive antibiotics for those getting a cesarean section.

Even public health officials acknowledge they were taken aback by the studies.

“Nobody could have been more surprised than I was when we got the results,” said Dr. Omrana Pasha of Aga Khan University in Pakistan, who led a study of maternal health interventions in six countries in Latin America, Africa and Asia.

“In clinical medicine, we would not prescribe a drug unless multiple trials show that it works,” she added. “The FDA won’t allow a drug to be marketed without that evidence. But things are different in public health.”

At an international meeting of U.N. partners starting Monday in South Africa, health officials are getting ready to ask donors for even more money to pour into maternal health programs. Since 2009, the U.S. has invested more than $13 billion in maternal and child survival, hoping to save lives by supporting “high-impact” health interventions.

According to the research papers, including one done in 30 countries that tracked more than 300,000 women, scientists found no link between the supposedly life-saving interventions and the death rates of women giving birth. Areas that used the interventions didn’t have better survival rates for mothers than areas that didn’t.

The two papers published last year are the biggest to assess the effectiveness of maternal health strategies, although smaller studies have previously suggested the methods help. But they gained little traction, perhaps because there doesn’t appear to be an easy fix.

Experts, meanwhile, are largely stumped as to why their methods failed to prevent deaths.

“We assume that if women get these things, they will be saved. But it’s too simple to say one plus one equals two,” said Dr. Marleen Temmerman, director of WHO’s maternal health department.

She isn’t convinced the interventions don’t work. She suspects there were problems implementing the strategies.

“Maybe the health facility has the medicine, but the man who has the key to the cupboard is gone,” she suggested.

Temmerman also said it would be dangerous if donors abruptly slashed their support for maternal health initiatives.

“The message is not to stop investing, it’s to invest money more wisely,” she said.

Some experts said existing plans should be adjusted.

“These essential interventions are important but they are not enough,” said Sandrine Simon, a public health adviser at Doctors of the World charity. “This is about more than buying the right medicines.”

But others said major changes were required to save more women.

“We need to be more honest and serious about past failures otherwise we will keep making the same mistakes,” said Bill Easterly, an economist at New York University. “It’s not just the fault of countries receiving aid who aren’t implementing the technology properly, it’s the fault of Western aid agencies and donors who are not trying hard enough to get it right.”