Current understanding of adolescent fertility is limited by an almost exclusive reliance on one fertility measure—the birth rate per thousand adolescents aged 15-19 (or teen birth rate). The teen birth rate’s falls short because it cannot: account for childbearing throughout all adolescence, convey information about age at first birth, examine patterns of repeat births in adolescence, or look at spacing between repeat adolescent births. All of these are important aspects of adolescent fertility, particularly among the most vulnerable and youngest groups of girls. Without more dynamic fertility measures, these vulnerable girls remain largely invisible. Fortunately, existing data from Demographic and Health Survey (DHS) and Multiple Indicator Cluster Surveys (MICS) combined with specially-adapted demographic measures can shed light on decades of hidden patterns of adolescent fertility. These new measures are particularly powerful for highlighting childbearing trends among the youngest adolescents, those 14 years and younger, for whom nationally-representative adolescent fertility research is sparse. The long-term perspective is critical for distinguishing between stubbornly entrenched patterns or dramatic progress in adolescent fertility against a backdrop of declines in overall fertility and other improvements in human development over the last half century across the globe.