Adolescent sexuality refers to sexual feelings, behavior and development in adolescents and is a stage of human sexuality. Sexuality is a vital aspect of teens' lives. The sexual behavior of adolescents is, in most cases, influenced by their culture's norms and mores, their sexual orientation, and the issues of social control such as age of consent laws. In humans, mature sexual desire usually begins to appear with the onset of puberty. Sexual expression can take the form of masturbation or sex with a partner. Sexual interests among adolescents, like adults, can vary greatly. Sexual activity in general is associated with a number of risks, including sexually transmitted diseases (including HIV/AIDS) and unwanted pregnancy. This is particularly true for adolescents as most are not emotionally mature or financially self sufficient. Teenage pregnancy Adolescent girls become fertile following the menarche (first menstrual period), which occurs in the United States at an average age of 12.5., although it can vary widely between different girls. After menarche, sexual intercourse (especially without contraception) can lead to pregnancy. The pregnant teenager may then miscarry, have an abortion, or carry the child to full term. Pregnant teenagers face many of the same obstetrics issues as women in their 20s and 30s. However, there are additional medical concerns for younger mothers, particularly those under 15 and those living in developing countries; for example, obstetric fistula is a particular issue for very young mothers in poorer regions. For mothers between 15 and 19, age in itself is not a risk factor, but additional risks may be associated with socioeconomic factors; for example pregnant teenagers are less likely than women over 20 to receive early prenatal care. Worldwide, rates of teenage births range widely. For example, sub-Saharan Africa has a high proportion of teenage mothers whereas industrialized Asian countries such as South Korea and Japan have very low rates.Teenage pregnancy in developed countries is usually outside of marriage, and carries a social stigma; teenage mothers and their children in developed countries show lower educational levels, higher rates of poverty, and other poorer "life outcomes" compared with older mothers and their children. In the developing world, teenage pregnancy is usually within marriage and does not carry such a stigma. The following percentage of 15 years old boys and girls, from each participating country, reported ever having had sexual intercourse: Prevalence of Participants Reporting Ever Having Had Sexual Intercourse by Country and Sex According to the 2002 World Health Organization Health Behaviour in School-aged Children Study: Austria boys 21,7% girls 17,9% Canada boys 24,1% girls 23,9% Croatia boys 21,9% girls 8,2% England boys 34,9% girls 39,9% Estonia boys 18,8% girls 14,1% Finland boys 23,1% girls 32,7% Flemish Belgium boys 24,6% girls 23,0% France boys 25,1% girls 17,7% Greece boys 32,5% girls 9,5% Hungary boys 25,0% girls 16,3% Israel boys 31,0% girls 8,2% Latvia boys 19,2% girls 12,4% Lithuania boys 24,4% girls 9,2% Macedonia boys 34,2% girls 2,7% Netherlands boys 23,3% girls 20,5% Poland boys 20,5% girls 9,3% Portugal boys 29,2% girls 19,1% Scotland boys 32,1% girls 34,1% Slovenia boys 28,2% girls 20,1% Spain boys 17,2% girls 13,9% Sweden boys 24,6% girls 29,9% Switzerland boys 24,1% girls 20,3% Ukraine boys 47,1% girls 24,0% Wales boys 27,3% girls 38,5% Contraceptive use Among Indian girls, "misconceptions about sex, sexuality and sexual health were large. However, adolescents having sex relationships were somewhat better informed about the sources of spread of STDs and HIV/AIDS." While 40.0% of sexually active girls were aware that condoms could help prevent the spread of HIV/AIDS and reduce the likelihood of pregnancy, only 10.5% used a condom during the last time they had intercourse.