If it is calculated for the exact age of 20 years, it indicates the probability of becoming a modter during adolescence. When censuses are used as a source, die numerator is mothers aged 15 tol9 who report diat they have had one or more live birdis. When specialized surveys are used (Demographic and Health Surveys or Intemarional Reproductive Health Surveys), die numerator normally corresponds to women aged 15 to 19 who report diat diey have had one or mote live births and women who are pregnant for the first time. In both cases, die denominator is all women aged 15 tol9.