Nicaragua has one of the highest adolescent fertility rates in Latin America and in the Caribbean. However, studies on adolescent pregnancies are limited. This study investigates the mechanism of early fertility among women aged 15 to 24 in northern central and eastern regions (NC-E) and the Pacific region (PAC), using data from the Nicaraguan Demographic and Health Survey 2011/12 ( N = 2,600). Structural equation modeling analysis was conducted in NC-E and PAC to examine the associations between exogenous variables (ethnicity and residence), mediators (education, sexuality education, knowledge and attitudes on pregnancy prevention, and sexual behaviors), and outcome (early fertility). The results showed educational attainment and sexual behaviors were crucial mediators of early fertility in NC-E and PAC, whereas sexuality education was only in NC-E. Residence was an exogenous variable in both groups, whereas ethnicity was not. Although educational attainment and sexuality education would improve knowledge, they did not contribute to reducing risky sexual behaviors. Further discussions on ethnic differences and variables measuring the actual decision-making related to risky sexual behaviors are suggested.