Human reproduction in crisis: causes unknown
Niels E Skakkebaeka niels.erik.skakkebaek@regionh.dk ∙ Lærke Priskorna ∙ Rune Lindahl-Jacobsenb ∙ Anna-Maria Anderssona ∙ David M Kristensenc ∙ Astrid Linnea Becka ∙ et al.
Fertility rates have plummeted, making human reproduction below replacement level across all industrialised regions (Organization for Economic Cooperation and Development fertility trends are illlustrated in appendix p 2).1
In line with the tradition of demographic research, the decline in fertility rates has been assumed to reflect a cultural transition due to social and economic changes of modern times.2 However, this theory has not provided concrete evidence linking specific socioeconomic factors to the decline in fertility rates. Other hypotheses suggesting that lower fecundity (the biological ability to reproduce) could contribute to lower fertility rates have typically been overlooked in demographic research.2,3
Governments have often responded to the proposals of demographic studies to lift fertility rates by providing special so-called baby bonuses. However, such programmes have not resulted in higher birth rates.4
The rapidly diminishing number of children and young people is already reshaping societies (predicted population trends are depicted in appendix p 3).5
We should not restrict our search for causes of low birth rates by studying only socioeconomic hypotheses. Important biological questions remain to be answered. Why is the demand for medically assisted reproduction (MAR) increasing all over the world, independent of geography, social status, workplace, religion, and political systems?6 Why has the comprehensive unassisted pregnancy rate (including the rate of induced legal abortions) been decreasing? What is the role of declining semen quality that has been reported from all regions of the world?7 Do the chemicals we detect in our organs8 from exposure to contamination from food, indoor environment, and air pollution9 play a role? Although these questions might appear straightforward, the answers remain elusive, and the reason for this is simple: the necessary large field studies of representative samples of people from the general population have never been done.
Despite sharing a common research focus, demographers and reproductive biologists have rarely collaborated. Their differing perspectives are evident even in their understanding of the term fertility: for demographers, it refers to the number of births, whereas in medical fields it denotes the ability to reproduce (ie, fecundity). As a result, couples experiencing infertility conceiving through MAR would, in a demographic context, likely be classified as fertile, even though they—after treatment—remain infertile in a medical and biological sense. It has been documented that more than 10% of all children in Denmark are now born as a result of MAR.10 And yet, MAR remains absent from the annual statistics on birth rates.
Scientists in reproductive medicine and socioeconomic scientists working in demography should collaborate to bridge the gaps between their research fields and design necessary large-scale, multidisciplinary field studies to identify the socioeconomic and biological causes behind the present crisis in human reproduction. In Scandinavian countries, electronic communication with respect to data safety and privacy can facilitate this study design.
If low birth rates ultimately stem from voluntary childlessness, socioeconomic conditions, current uncertainties about the future, or any combination of these, we should perhaps not worry, as such trends might change with time. However, if the declining fertility rates signal a lasting crisis—driven by an increasing number of young people with failing reproductive systems due to environmental problems—then urgent action is needed. It is time for our health authorities and governments to respond. Future generations depend on it.
- DFM June 18, 2025, 2:03 pm