Periodic Reporting for period 2 - BIC.LATE (Biological, Individual and Contextual Factors of Fertility Recovery)
Okres sprawozdawczy: 2023-03-01 do 2024-08-31
While much research has been done on why people delay having children in low fertility countries, it is not yet well understood what helps or hinders people to have children later in life (in their 30s and 40s).
(1) Later reproductive age is very specific, with a rapid decline in reproductive capacity from the mid-30s and a steeper decline in the 40s. This means that as an increasing proportion of the population wishes to have children later, more and more people will potentially face a biological constraint on their childbearing prospects. For this reason, the project examines reproductive experiences at different ages, including the increase in biological limits with age and the resulting increase in the use of medically assisted reproduction (MAR).
(2) People who have delayed childbearing are at a different stage in their lives than those who have children earlier. For example, they will have worked longer, they may already have had more than one partner, their health may be declining, or their parents may be at an age when they need more care and support. Accordingly, we explore the reproductive experiences of those who have their first child in their 30s or later, how individual circumstances seem to unfold to make birth possible, and the fine line between delaying and foregoing childbearing.
(3) The context of fertility at later ages differs from that at earlier ages. People may perceive pressures around reproductive timing that make them want to have children faster or not at all. To better understand perceptions of late fertility, we examine laws and attitudes around the age of childbearing or the use of MAR. We then link the normative and economic environment, as well as markers of gender balance, to late fertility.
(4) Finally, the observed reproductive age limits (which combine biological, technological and normative aspects) may discourage people from having children, but there is little evidence on the extent to which delaying the first child leads to lower fertility levels. We explore this issue by linking reproductive age limits to completed fertility, and by examining the experience of infertility as a vector for having a smaller family than intended.
The project will improve the understanding of the main drivers of fertility at later ages across Europe in times of later family formation. It contributes to the development of an important area of research at the interface between demography and epidemiology.
(1) Later reproductive age is very specific, with a rapid decline in reproductive capacity from the mid-30s and a steeper decline in the 40s. This means that as an increasing proportion of the population wishes to have children later, more and more people will potentially face a biological constraint on their childbearing prospects. For this reason, the project examines reproductive experiences at different ages, including the increase in biological limits with age and the resulting increase in the use of medically assisted reproduction (MAR).
(2) People who have delayed childbearing are at a different stage in their lives than those who have children earlier. For example, they will have worked longer, they may already have had more than one partner, their health may be declining, or their parents may be at an age when they need more care and support. Accordingly, we explore the reproductive experiences of those who have their first child in their 30s or later, how individual circumstances seem to unfold to make birth possible, and the fine line between delaying and foregoing childbearing.
(3) The context of fertility at later ages differs from that at earlier ages. People may perceive pressures around reproductive timing that make them want to have children faster or not at all. To better understand perceptions of late fertility, we examine laws and attitudes around the age of childbearing or the use of MAR. We then link the normative and economic environment, as well as markers of gender balance, to late fertility.
(4) Finally, the observed reproductive age limits (which combine biological, technological and normative aspects) may discourage people from having children, but there is little evidence on the extent to which delaying the first child leads to lower fertility levels. We explore this issue by linking reproductive age limits to completed fertility, and by examining the experience of infertility as a vector for having a smaller family than intended.
The project will improve the understanding of the main drivers of fertility at later ages across Europe in times of later family formation. It contributes to the development of an important area of research at the interface between demography and epidemiology.
We estimated curves showing the decline in fertility with age since first trying to get pregnant in Germany. Female sterility risks by age appear to be similar when calculated with contemporary or historical data, but our confidence intervals are large. MAR use improves the chances of having children, but the decline in fertility with age is still deep for women. The decrease is smaller for men.
Our studies expose the socioeconomic disparity in MAR births in the US, more frequent among highly educated men and women. They highlight the increasing dependence of fertility levels on MAR births in Australia. In Spain, still, MAR use remains unsystematic as people postpone entry into adulthood. In exploring misconceptions about MAR, we find that in the USA, women with more confidence in MAR are more likely to postpone childbearing.
As a reminder of the basics of reproduction, preliminary results in Germany suggest that successful pregnancy among people trying to have a child is more likely if they have sex at least 2-3 times a week. In Australia, a decline in self-perceived physical or mental health is associated with a decline in fertility expectations, effect reinforced by age. Adults who became carers for their elderly parents were also more likely to reverse their fertility intentions. The birth of a child with a disability seems to both slow down and reduce the transition to another birth in France.
We showed across Europe that the higher prevalence of late fertility in cities is connected to higher female education, greater wealth and a higher share of employment in high technology sectors. Ongoing work also shows a significant link between geographical proximity and the rise in late fertility across European regions. The study of legislation on the use of MAR and its age limits shows that in most countries the legal framework is not supportive of late births, but that in some contexts permissive laws and free access to MAR are used to promote fertility.
Ongoing research using a microsimulation based on Belgian data shows that postponing first births strongly reduces transitions to second and higher order births, and that beyond a modal age at first birth of 33 years, it also starts to increase the proportion of people who remain childless. Together with our empirical study of biological childlessness, this suggests that in countries where first births occur very late, such as Italy or Spain, childlessness is already being fuelled by fertility postponement.
Our studies expose the socioeconomic disparity in MAR births in the US, more frequent among highly educated men and women. They highlight the increasing dependence of fertility levels on MAR births in Australia. In Spain, still, MAR use remains unsystematic as people postpone entry into adulthood. In exploring misconceptions about MAR, we find that in the USA, women with more confidence in MAR are more likely to postpone childbearing.
As a reminder of the basics of reproduction, preliminary results in Germany suggest that successful pregnancy among people trying to have a child is more likely if they have sex at least 2-3 times a week. In Australia, a decline in self-perceived physical or mental health is associated with a decline in fertility expectations, effect reinforced by age. Adults who became carers for their elderly parents were also more likely to reverse their fertility intentions. The birth of a child with a disability seems to both slow down and reduce the transition to another birth in France.
We showed across Europe that the higher prevalence of late fertility in cities is connected to higher female education, greater wealth and a higher share of employment in high technology sectors. Ongoing work also shows a significant link between geographical proximity and the rise in late fertility across European regions. The study of legislation on the use of MAR and its age limits shows that in most countries the legal framework is not supportive of late births, but that in some contexts permissive laws and free access to MAR are used to promote fertility.
Ongoing research using a microsimulation based on Belgian data shows that postponing first births strongly reduces transitions to second and higher order births, and that beyond a modal age at first birth of 33 years, it also starts to increase the proportion of people who remain childless. Together with our empirical study of biological childlessness, this suggests that in countries where first births occur very late, such as Italy or Spain, childlessness is already being fuelled by fertility postponement.
This project brings together many elements on how biological, individual and contextual factors contribute to fertility in later life. The inclusion of the reproductive dimension in fertility research is extremely rich and this is a major contribution of this project. The increasing dependence of fertility levels on medically assisted reproduction is an important issue to be addressed in tomorrow's societies, as is the fact that a growing group of women and couples will not have the children they want. However, it appears that the social and economic context is of paramount importance to such developments, and that although highly educated women postpone childbearing more, they are also more resilient to change and more successful at having children later in life.
Another breakthrough relates to the calculation of infertility curves by age: the first results showing that the levels of infertility estimated on the basis of contemporary data for women are very close to the levels estimated on the basis of historical data are very important because they refute the hypothesis that we are in an "infertility crisis" (e.g. the sperm crisis narrative). People are still physiologically capable of having as many children as before if they try early enough. Updating the calculations with the latest pairfam waves and modelling them should allow us to estimate a curve by single year of age and with narrower confidence intervals at higher ages, for both men and women and depending on the use of assisted reproduction.
In this project, we have finally been able to link fertility timing (i.e. delayed fertility) and fertility quantum (i.e. the average number of children) clearly and "mechanically" using microsimulation. Again, this was achieved by integrating epidemiological evidence (the existence of reproductive age limits) with demographic thinking (the microsimulation modelling birth transition and completed cohort fertility). In the next phase of the project, we would like to extend this work to other countries with low fertility. In this way, we want to understand at what stage of fertility postponement fertility starts to decline due to foregone births. This should also help us to assess indirectly what proportion of women may have to forego childbearing due to excessive postponement, a fundamental issue.
Another breakthrough relates to the calculation of infertility curves by age: the first results showing that the levels of infertility estimated on the basis of contemporary data for women are very close to the levels estimated on the basis of historical data are very important because they refute the hypothesis that we are in an "infertility crisis" (e.g. the sperm crisis narrative). People are still physiologically capable of having as many children as before if they try early enough. Updating the calculations with the latest pairfam waves and modelling them should allow us to estimate a curve by single year of age and with narrower confidence intervals at higher ages, for both men and women and depending on the use of assisted reproduction.
In this project, we have finally been able to link fertility timing (i.e. delayed fertility) and fertility quantum (i.e. the average number of children) clearly and "mechanically" using microsimulation. Again, this was achieved by integrating epidemiological evidence (the existence of reproductive age limits) with demographic thinking (the microsimulation modelling birth transition and completed cohort fertility). In the next phase of the project, we would like to extend this work to other countries with low fertility. In this way, we want to understand at what stage of fertility postponement fertility starts to decline due to foregone births. This should also help us to assess indirectly what proportion of women may have to forego childbearing due to excessive postponement, a fundamental issue.