Where's the best (and worst) country to be a mom?

Just 15 years ago, the United States was among the top 10 countries in the world to be a mother, but the U.S. has fallen to 31st on the list of 178 nations, a new report released Monday says.

According to Save the Children's 15th annual State of the World's Mothers Report, the risk that a 15-year-old girl will die in the U.S. during her lifetime from a maternal cause has soared 50 percent since 2000. The group cites multiple health studies as contributing factors - including an increase in high-risk pregnancies among mothers with obesity and hypertension.

Finland once again topped the organization's Mothers' Index, which is derived from health, educational and economic factors. Somalia - beset by both conflict and natural disaster - ranked at the bottom of the list. Across the globe, 56 percent of all maternal and child deaths occur in countries ravaged by war or disasters, the report said.

According to the report, in Somalia, more than 6 percent of women are likely to die of a maternal cause, while about 15 percent of children will die before their 5th birthday. By contrast, maternal deaths affect less than one in 12,000 women in Finland, and just one in 345 children will die before the age of 5.

Earlier this month, the United Nations said more than 200,000 Somali children under the age of 5 are "acutely malnourished."

"Nothing will stop a mother from trying to keep her children safe and protected," said Carolyn Miles, President and CEO of Save the Children, "But when disaster strikes, whether it's a war in Syria, a tornado in Oklahoma or a typhoon in the Philippines, women and children are at the greatest risk - 14 times more likely to die than men."

Mothers and children are particularly vulnerable in war-town countries. In Syria, for example, an estimated 1.4 million children and nearly 700,000 women have sought refuge in neighboring countries, while over 9 million people inside Syria need lifesaving humanitarian aid, the reports said. In December, the U.N. asked for $6.5 billion to deliver food, shelter and health care in Syria.

The report also cited "horrific abuses against women and children" amid civil war in the Democratic Republic of Congo. According to Save the Children, it is statistically more dangerous to be a woman or child than an armed fighter in the Democratic Republic of Congo, which ranked second to last in the rankings.

However, the report did cite some good news in Afghanistan. The country, which ranked dead last in the rankings in 2010 and 2011, moved up 32 places this year. The report credited better midwife training, immunization programs and more educational opportunities for girls for the progress.

Save the Children called for better humanitarian access in war zones as well as improved preparedness in regions prone to natural disasters.

"Failure to address basic human needs has been both a cause and a consequence of conflict in countries like Central African Republic, Somalia and Sudan," the report concluded. "And the hardest hit families in any disaster - be it 'natural' or man-made - tend to be the poorest of the poor, mostly women and children."

With Mother's Day looming, Miles urged more focus on mothers who live in countries plagued by humanitarian crises.

"While we celebrate the mothers in our lives this week," she said, "we should also advocate for those who are in urgent need."