The birthrate among teenagers in the United States (US) dropped 8% in 2015 to another record low, the latest sign of major progress in efforts to reduce teen pregnancies, a federal health agency reported on Thursday.The rate in 2015 fell to 22.3 births per 1,000 teenage girls aged 15 to 19, down from 24.2 births in 2014, the US Centre for Disease Control and Prevention (CDC) said in a preliminary study based on birth certificate data. The birthrate for teenagers has dropped 64% from its peak in 1991, the agency said. The 2015 rate was the lowest since the federal government began tracking teenage births in 1940.”We’re reaching record lows every year,” said Brady Hamilton, one of the authors of the study. “These declines are absolutely astounding.” The number of teen births fell to 229,888 last year from 249,078 in 2014, the CDC said.The agency has cited a decline in teenage sexual activity and an increase in the use of birth control as factors in the steady drop in teen births. Experts have cited reality television shows on teen mothers as a factor as well. “This nation has made remarkable, off-the-chart success on a pressing social issue that many of us considered unsolvable,” said Bill Albert, spokesman for the non-profit National Campaign to Prevent Teen and Unplanned Pregnancy.Teen pregnancy can lead to lower educational achievement and increase the risk of poverty, Albert said. Only about four in 10 girls who have a child in high school go on to graduate, he pointed out. According to a report published last year by the Journal of Adolescent Health, the United States had the highest teen pregnancy rate among 21 countries with complete statistics, with 57 pregnancies per 1,000 females from 2008 to 2011. Switzerland had the lowest rate at eight per 1,000.The overall number of US births declined slightly in 2015 to 3.97 million from 3.98 million the year before, the CDC said. The drop followed an increase in 2014, the first since 2007. The rate for caesarean deliveries dropped in 2015 for the third year in a row, declining to 32% from 32.2% in 2014.