"Initiation of sexual intercourse puts a teenager at risk for unintended pregnancy and sexually transmitted infection. After declining between 1991 and 2001 (54% to 46%), sexual experience among U.S. high school students has remained at 46–47% from 2001 to 2005. Over 750 000 U.S. adolescents (aged 15–19) become pregnant each year, and over 28% of these pregnancies end in abortion. Most adolescent pregnancies (82%) are unintended. A recent analysis of the decline in U.S. adolescent pregnancy rates between the 1995 and 2002 National Surveys of Family Growth demonstrated that 86% of the decline was due to improved contraceptive use (less nonuse, increased use of condoms and highly effective hormonal methods, and increased use of dual methods), and only 14% due to declines in sexual behavior. Although pregnancy rates have declined, the United States still leads the developed world in adolescent (aged 15–19) birth rates, with 42 births per 1000 women in 2004. By comparison, adolescents in the United Kingdom had 27 births per 1000 women; in Italy, seven births per 1000 women; and in the Netherlands, five births per 1000 women."