Teenage pregnancy refers to pregnancy in a female under the age of 20. A pregnancy can take place at any time before or after puberty, with menarche (first menstrual period) normally taking place around the ages 12 or 13, and being the stage at which a female becomes potentially fertile. Teenage pregnancy depends on a number of social and personal factors. Teenage pregnancy rates vary between countries because of differences in levels of sexual activity, general sex education provided and access to affordable contraceptive options. Worldwide, teenage pregnancy rates range from 143 per 1000 in some sub-Saharan African countries to 2.9 per 1000 in South Korea. Pregnant teenagers face many of the same obstetrics issues as women in their 20s and 30s. There are however, additional medical concerns for mothers age 14 or younger. For mothers between 15 and 19, risks are associated more with socioeconomic factors than with the biological effects of age.However research has shown that the risk of low birth weight is connected to the biological age itself, as it was observed in teen births even after controlling for other risk factors . In developed countries, teenage pregnancies are associated with many social issues, including lower educational levels, higher rates of poverty, and other poorer life outcomes in children of teenage mothers. Teenage pregnancy in developed countries is usually outside of marriage, and carries a social stigma in many communities and cultures.