Actress Ashley Judd appears at a news conference at United Nations headquarters upon her appointment as the UN Population Fund (UNFPA) Goodwill Ambassador in New York, March 15, 2016. [Photo/Agencies]

Judd said that the "solution lies in massive attitudinal shifts towards girls and women," and can be helped by access to secondary education.

"For every additional year of secondary education a girl's income increases by 10 to 20 percent, that supports her family and actually creates increases in a country's GDP," she said, referring to gross domestic product.

Osotimehin described other ways that girls are disadvantaged within the family, particularly in poor countries and conflict zones.

"More than 300,000 women die every year giving life," said Osotimehin. Sixty percent of the women who die from pregnancy or childbirth related causes are in emergency or so-called fragile situations, such as refugees and other women fleeing conflict, he said.