The article substantiates the possibility of considering fertility, traditionally understood in demography as a socio-biological process, as an object of constitutional regulation and legal research. Fertility, which is a quantitative indicator of live births, cannot be studied in isolation from the events that influence it, such as family planning, pregnancy, the perinatal period, and the formation of reproductive attitudes. It is proposed that fertility as an object of constitutional regulation must be considered through the prism of the concept of interests, differentiated according to the subjects: personal, state, and public. The state interest is linked to demographic policy and the need to achieve targets. Particular attention is paid to the issue of the proportionality of such policies, when the state's pursuit of strategic goals may conflict with human rights. The public interest reflects the involvement of citizens, including through the activities of public associations, in the processes of fertility regulation. Personal interest is expressed in ensuring the full realization of reproductive rights. The author concludes that constitutional and legal analysis and the impact on fertility should be carried out taking into account not only quantitative indicators, but also reproductive rights affected by public regulation, which will avoid excessive state interference in the private lives of citizens.