HANOI, Sept 9 (Reuters) – The ratio of boys born in Vietnam compared with girls has grown at an unusually rapid pace in recent years and could lead to a rise in sex work and trafficking, the United Nations said.

The sex ratio at birth was 112.1 male births per 100 female births in 2008, up from an estimated 106.2 in 2000, the U.N. Population Fund (UNFPA) said in a report.

With growth since 2006 of one percentage point per year, the ratio might cross the 115 mark within three years, it said.

By 2035, the surplus of adult men would be 10 percent or more of the female population if the sex ratio did not return to 105 male births per 100 females, it said.

“Scarcity of women would increase pressure for them to marry at a younger age, there may be a rising demand for sex work and the trafficking networks may also expand in response to this imbalance,” UNFPA said.

“Examples of gender-based violence and human trafficking have already been observed in Vietnam and point to some of the risks faced by vulnerable girls and women.”

A key factor behind the rise in the number of male births to female births is increasing access to sex-determination and sex-selection technology, “which has allowed couples to pursue their desire for one or more sons”, the UNFPA said.

Vietnam, which has had an agriculture-based economy for centuries, has a population of nearly 86 million with a strong preference for sons.