I want to return to the conceptual framework for adolescent health that Susan introduced in an earlier lecture. We've previously introduced the idea of adolescence as a phase of life that begins with the biological event at puberty, and ends with a series of social role transitions that mark entry into adulthood. These role transitions have become more complex. Once upon a time, it was about marriage and parenthood. Now, it's about completing education, finding employment that gives financial independence from one's family of origin. And even achieving the cognitive and emotional capacity to be independent. In the following lectures, I shall be shifting attention to some of the role transitions that have set the upper age boundary of adolescence. I want to begin by addressing the transition that through human history has most defined the transition to adulthood, that is, marriage and parenthood. That is about forming a family of one's own. In this slide from an earlier lecture, we illustrated the changing shape of adolescence over the past 200 years in many of today's high income countries. Of note is the changing gap between the onset of sexual activity and settling into marriage or life partnerships. In many high income countries this is now well over a decade. Even greater is the gap between the events that mark reproductive capability and having a first child. For girls with early puberty the gap between menarche, and having a first child is commonly over two decades. Tied to the good provision of health care, including good access to contraception, this has transformed risks for reproductive and maternal health in the adolescent years. In low income countries, similar trends have occurred. The potential for gains in adolescent sexual and reproductive health are huge, but cannot be taken for granted. So, let's try to understand first what are the recent trends. The following graph derives from the United Nations Population Division. It illustrates changes over the last 15 years in the percentage of young women, aged 15 to 19, who are married. The data come from high, middle, and low income countries. The diagonal line allows us to see which countries have managed to reduce levels of teenage marriage since 1990. Countries below the line are trending toward lower rates of teenage marriage 15 years later. The majority of countries where the high or low income have followed a similar trend. High income countries, those with the blue circles, have much lower rates of teenage marriage at both points in time. Asian countries, have tended to have higher rates, but have had very strong trends to lower rates over the last 15 years. And it should be fairly clear that Sub-Saharan African countries continue to have the highest rates of teenage marriage. Mostly in excess of 20%, and in some, in excess of 50%. However, even within these countries, most are moving toward lower rates of teenage marriage. It's not just early marriage where there are very different pictures in different places. This global map of birth rates for girls aged 15 to 19 illustrates some of the huge geographic variations. In most of western Europe and in a range of other high middle income countries including China, birth rates to teenage girls are low. The highest rates are in Sub-Saharan Africa. And in a few countries of Latin America and South Asia, teenage birth rates also remain very high. But, just as rates of adolescent marriage have declined, so too have rates of adolescent births have also declined over the last 15 years in the great majority of countries, whether it be in low adolescent fertility countries of Europe and North America, intermediate adolescent fertility countries of Latin American and Asia. Or the high adolescent fertility countries of Sub-Saharan Africa, the trend toward lower adolescent fertility is clear with the great majority of countries falling below the diagonal line. I mentioned earlier that one of the striking changes in high income countries has been the rise of the sexually active, unmarried adolescents in young adulthood. So I want to ask the question, to what extent has this occurred in low and middle income countries? The answer is quite a lot. In these selected countries that all have high adolescent birth rates, many young adult women report that their first sexual experience was outside of marriage. Indeed is Swaziland, Liberia, and the Congo, over 50% women report their first sexual experience outside of marriage. Because these data derive from household surveys where under reporting is likely to be common, the actual rates of sexual activity before marriage are likely to be much higher again than I'm showing here. The rise of sexually active unmarried adolescents, in a context of limited access to contraception, matters. The association between having a birth outside of marriage and the proportion of adolescents who are sexually active prior to marriage is clear in this graph. The clearest trends are in countries with high adolescent birth rates. But they are also evident in those with intermediate levels of adolescent fertility. It is clear that these widespread changes in role transition into marriage and parenthood have major implications for sexual, reproductive and maternal health of adolescence in young adults. In the next lecture, I will address some of the essential actions that we in health, need to promote in order to ensure that young people and young women in particular achieves the gains that we have seen in many high income countries. And avoid the adverse health and social consequences that might otherwise occur.