Advanced maternal age

Advanced maternal age, in a broad sense, is the instance of a woman being of an older age at a stage of reproduction, although there are various definitions of specific age and stage of reproduction. The variability in definitions is in part explained by the effects of increasing age occurring as a continuum rather than as a threshold effect.

Average age at first childbirth has been increasing, especially in OECD countries, among which the highest average age is 32.6 years (South Korea) followed by 32.1 years (Ireland and Spain). In a number of European countries (Spain), the mean age of women at first childbirth has crossed the 30 year threshold. This process is not restricted to Europe. Asia, Japan and the United States are all seeing average age at first birth on the rise, and increasingly the process is spreading to countries in the developing world such as China, Turkey and Iran. In the U.S., the average age of first childbirth was 26.9 in 2018.

Advanced maternal age is associated with adverse maternal and perinatal outcomes. Possible maternal complications due to advanced maternal age include preterm labor, pre-eclampsia, gestational diabetes mellitus, stillbirth, chromosomal abnormalities, spontaneous miscarriage and cesarean delivery. Advanced age can also increase the risk of infertility. Some of the possible fetal outcomes due to advanced maternal age include admission to neonatal intensive care units (NICU), intrauterine growth restrictions, low Apgar score, chromosomal abnormalities and infants smaller for gestational age. The corresponding paternal age effect is less pronounced.

Having children later was not exceptional in the past, when families were larger and women often continued bearing children until the end of their reproductive age. What is so radical about this recent transformation is that it is the age at which women give birth to their first child, which is becoming comparatively high, leaving an ever more constricted window of biological opportunity for second and subsequent children, should they be desired. Unsurprisingly, high first-birth ages and high rates of birth postponement are associated with the arrival of low, and lowest-low fertility.

This association has now become especially clear, since the postponement of first births in a number of countries has now continued unabated for more than three decades and has become one of the most prominent characteristics of fertility patterns in developed societies. A variety of authors (in particular, Lesthaeghe) have argued that fertility postponement constitutes the "hallmark" of what has become known as the "second demographic transition".^{[citation needed]}

Others have proposed that the postponement process itself constitutes a separate "third transition". On this latter view, modern developed societies exhibit a kind of dual fertility pattern, with the majority of births being concentrated either among very young or increasingly older mothers. This is sometimes known as the "rectangularisation" of fertility patterns.

There are many factors that may influence childbearing age in women, although they are mostly correlations without certain causations. For instance, older maternal age at first childbirth is associated with higher educational attainment and income.

Two studies show that generous parental leave allowances in Britain encourage young motherhood and that parental-leave allowance reduces postponement in Sweden.