The correct answer is: "Birth rate"
The birth rate is an important demographic indicator that is computed by taking into account the number of live births that have taken place, per 1,000 members of a population, during a certain period of time. This rate, together with the mortality and migration rates, is used to compute population growth.
Several techniques can be used to gather the data about the number of births, such as the universal registration system for births, deaths, and marriages, population censuses, or the results of estimation procedures performed using specialized demographic techniques.