The relationship between age at first birth and overall fertility in developing countries like Bangladesh is generally an underdeveloped area as far as demographic research is concerned. Fertility analysts generally assume that child bearing only occurs within marriage. Then they treat age at first marriage to be a major proximate determinant of fertility. Result shows that women in Bangladesh engage in sexual activities at an early age before 15 years and most use modern methods (43%) for birth control. Most of women use specific pills method. Islam religion has a more tendency to marry at age before 15 years. The incidence of primary sterility for formerly married women; it is increases as duration of marriage increase and for currently married women; it is decreases with increase in duration of marriage. Findings need to be scientifically used in suitable programs addressing the case of fertility control in the developing countries as well as in Bangladesh.