Poverty and under-education dampen contraception use in Nepal but another factor may be more intractable: Deeply held cultural preferences for sons over daughters.

The cross-sectional study was based on data from the 2011 Nepal Demographic and Health Survey, which found that only one in five married adolescent and young women used modern contraception. Rates were lowest among women who resided in rural areas, lacked education or social status, were married as minors or had no sons.

Researchers found that geography (urban versus rural), age and levels of education, wealth and social status all predictably influenced whether Nepalese women used birth control. Young wives in Nepal were among those least likely to use contraceptives, 24 percent of wives ages 20-24 and just 14 percent of wives ages 15 to 19 years old. These low percentages, said first author Anita Raj, PhD, professor of medicine in the U.C. San Diego School of Medicine, were particularly notable among young wives who did not have any sons.

'Daughter aversion' remains a cultural bias in central and south Asian countries. Part of the reason is financial. Males traditionally enjoy greater economic opportunity.  

"But tradition also says sons take care of parents," Raj said. "Daughters are supposed to leave the family and become the daughter of the in-laws, no longer the daughter of the parents. Practices like that are going to affect investment in your daughters."

The latter effect may be due, in part, to the influence of older generations. Americans may lament that we don't 'respect our elders' as much as Asia, but we also don't teach young women self-loathing.

"Even after adjusting for child marriage, you see it. Girls who marry younger may be more vulnerable to son preference because they are more likely to have their reproductive decision-making affected – or controlled – by older husbands and in-laws, both of whom may desire sons from these young wives," she said.

"Until girls are valued as much as boys in families, we will continue to see these findings. We hoped generations (and modernization) would make it better, but this study is with young mothers and demonstrates that the beliefs are being carried into the youngest generation of child-bearers."

Raj said improved contraception use is linked to reducing maternal and infant or child mortality rates because younger mothers are more at risk.