The United Nations expects the world's population to increase from slightly more than 7 billion today to 9.6 billion by 2050. Almost all of the growth will occur in developing regions, especially Africa. For the most part, people in developed countries—where population is expected to remain largely unchanged over the coming decades—have consistent access to family planning resources and education about sexual health. (Even so, what the United Nations calls "low-fertility countries" have their own challenges: A recent Brookings Institution report found that a poor woman in the United States is more than five times as likely as an affluent woman to have an unintended birth.) The reasons population continues to climb in some areas of the world are varied and often tradition-bound. Here are a few examples and some ways they are being addressed.

Preference for male offspring 

In some societies, sons are expected to provide economic support, and girls are seen as economic liabilities to be married off, leading to the phenomenon of "son preference." This has been the underlying cause of Asia's "missing women" crisis: More than 100 million girls have died from malnourishment, lack of medical care, and infanticide. In some cultures where smaller families are preferred, sex-selective abortion has resulted in abnormally high ratios of boys to girls at birth. 

Solution: Raise the economic role of women. Education is key, as is increased access to contraception. Both helped drop Bangladesh's fertility rate from 6.3 births per woman 35 years ago to 2.2 in 2012. As one woman told Naila Kabeer, a London University professor of development studies, "The value of women is higher than that of men these days. They think that now they can earn money and have an education." In South Korea, son preference has declined dramatically, thanks to widespread education of females along with a healthy dose of antidiscrimination suits and equal-rights rulings.

Lack of education opportunities for women

In sub-Saharan Africa, 84 girls for every 100 boys are enrolled in secondary education. Child marriage, sexual violence, and inadequate sanitary facilities all factor in to why there are fewer education opportunities for women. 

Solution: A simple one is to ensure that girls have access to sanitary pads as well as hygienic locations at school in which to use them. That's the goal of the Procter & Gamble-sponsored program FemCare, an effort in Africa to cut down on girls' school absenteeism during menstruation. If girls stay in school longer, they are more likely to marry later and have fewer children.  

Patriarchal tradition

In many cultures, such as indigenous Guatemalan communities where large families are traditional, use of birth control is often not supported by husbands—and may even be seen as a sign of a wife's infidelity or prostitution. The result: Women may seek contraception without the knowledge of their partner, become victims of domestic violence, or seek unsafe abortions. While Guatemala's fertility rate has been declining steadily since the 1960s, today it is still 3.8 children per woman, the highest of any Latin American country and nearly double the global "replacement level" of 2.1. 

Solution: Involve males in family planning. The Women's International Network for Guatemalan Solutions (WINGS) runs a program called WINGS for Men to ensure that men participate constructively in their families' reproductive health. An analysis of a program in Africa run by the Kenya Medical Research Institute and the University of California at San Francisco found that men's receptivity to learning about birth control increased when family planning counseling and education was integrated into HIV clinics.

Matriarchal tradition

On the other side of the spectrum, in India a woman often lives with her mother-in-law, who influences how many children she'll have. That often translates into large families, with women opting for permanent sterilization (the most common form of birth control worldwide) only with a mother-in-law's consent, after the woman has delivered at least two grandsons. In the East Indian state of Bihar, families have an average of 3.5 children, the highest fertility rate in the country; only a third use any family planning method.

Solution: Educate the whole family. In Bangalore, India, a program called Dil Mil (an abbreviation of "Daughters-in-law, Mothers-in-law" and meaning "hearts together" in Hindi) fostered group discussions about family health among generations in individual households. As a result, women and their mothers-in-law were more likely to see each other as allies than adversaries. Even in areas without such resources, researchers have found that access to family planning information enables young couples to make their own contraceptive choices, particularly about whether and when to use reversible contraception methods.

Early and forced marriage

In developing countries, one in every three girls is married before age 18, and one in nine is married before age 15. Compared to other age groups, married adolescents have the lowest use of contraception, the highest number of children, an increased chance of high-risk pregnancies, and less access to education. Despite laws against child marriage, the practice remains widespread, in part because of gender inequality and intractable poverty: Marrying off a daughter early can relieve financial pressure in a poor family. 

Solution: In addition to enforcing laws against child marriage—Malawi, for example, raised the legal age for marriage to 18 this year—communities can come together to stop the practice. Aided by the locally based "community empowerment programs" of the nonprofit Tostan ("breakthrough" in the Wolof language of Senegal, Gambia, and Mauritania), the Senegalese village of Tankanto Maounde decided collectively to abandon the practice of female genital mutilation and the tradition of early marriage by committing to girls' educations—and celebrated the move with festive public declarations.

Misconceptions about birth control

Discussion about sexuality is often taboo, and reproductive health education is often absent throughout the world. It's no surprise, then, that myths and misunderstandings about family planning abound. Some common ones: oral contraceptives cause infertility and reduce a woman's sex drive, vasectomies cause cancer, and condoms may get lost in a woman's uterus or are to be used only for extramarital relations or prostitution. 

Solution: Train local health workers to debunk the gamut of misinformation. The Democratic Republic of the Congo's Integrated Health Project helps residents receive reproductive health counseling using behavior-change communication, a technique that emphasizes "reflective listening" and empathy with participants (think "there are no stupid questions"). IHP realized that community health workers often have the same misconceptions about family planning methods as their clients (one educator at a training asked, "Don't they contain a poison?"), which have to be addressed before workers can comfortably and accurately disseminate family planning messages.

This story has been corrected.