Vietnam, concerned that too many boys are being born, will destroy more than 30,000 copies of books instructing couples on how to have a baby of their desired sex, state-linked media said Friday.
The books include 27 titles and were seized last month, VietnamNet online news service said, citing officials.
Articles with the same content have been removed from seven websites, it said.
The trend will leave millions of Vietnamese men with difficulty finding wives if it continues, Deputy Prime Minister Nguyen Thien Nhan said, according to state media.
"Obviously, the imbalance in SRB (sex ratio at birth) results from son preference and sex selection abortion practices," the UN said.
Vietnam's prime minister has prohibited all practices of foetal sex determination and selection, the UN noted.
"Furthermore, continued efforts must be made to strengthen public education and to promote gender equality to enhance the important role of women both within families and society," the UN said.