Reproduction in a changing world.

Although the global population continues to increase, the total fertility rate in many high-income countries (HICs) is below replacement, a trend apparent over several decades. The timing and pace of this change will shape the age distribution in these countries, leading to an increasing proportion of older people. The well-established links of the "demographic transition" between improving female education and improved access to contraception continue to drive down the fertility rates in low-/middle-income countries. However, changes in the age distribution will not be as marked as in HICs in the coming decades. These relationships may now be changing in some HICs with greater prosperity at both the personal (in some sectors of society) and national levels, linked to an increase in the total fertility rates despite continuing trends toward older age at first birth. Key drivers in these countries include improved provision of free/low-cost childcare, paid parental leave, and higher paternal contributions to childcare. However, there is also an increase in the number of women who do not have children or who may be unable to complete their family plans. Coronavirus disease 2019 and environmental factors, including the increasing prevalence of obesity, add to pressures on the fertility rates. Variable knowledge of the realities of female reproductive aging, particularly by men, is also a contributing factor, and this complex mix has fueled the increase in the number of elective egg freezing. [ABSTRACT FROM AUTHOR]