Guillermo Antiñolo Gil
The study is methodologically sound. It draws on the Global Burden of Disease database (GBD 2023), covers 204 countries between 1990 and 2023, and applies standard, well-executed statistical tools. Its main contribution is to focus specifically on women aged 35 to 49 —the age range in which the biological decline in fertility truly matters— and to project the trend to 2036. The figures are striking in scale: around 53.6 million women in this age group were affected in 2023, with a projection close to 79.6 million by 2036, and a relative shift of the burden from less developed countries towards higher-income ones.
These numbers should nonetheless be read with caution, because the indicator does not measure quite what it appears to. The GBD’s “infertility prevalence” is a modelled figure that depends largely on whether a woman wishes to have children, seeks medical care, and has access to diagnostic services. In other words, it reflects health-care seeking and data-registration quality as much as biology. The clearest proof of this is the implausible disparity between similar countries: Belgium appears with 8,499 cases per 100,000 women and Germany with 2,195; Spain, at 2,226, falls well below the global average (6,907). I do not believe that a Belgian woman is four times more infertile than a German one. It is also worth clarifying what the “infertility rate” means: the study calculates it over all women aged 35–49, not only those trying to conceive, which is what is clinically understood by an infertility rate. Because the denominator is the whole female population in that age band, a mere rise in the number of women attempting pregnancy at older ages inflates the rate even if the per-attempt risk is unchanged; the increase should therefore not be read as a rise in the biological risk of infertility. Two further caveats apply. First, regarding the “burden”: the study expresses it in disability-adjusted life-years (DALYs), but infertility entails no mortality, so this burden consists entirely of a loss of quality of life; put another way, the GBD treats infertility itself as a disability to which it assigns a weight —a debatable value— and it should therefore not be compared with the burden of fatal diseases. Second, the study considers only female infertility and leaves out the male factor, which accounts for a substantial share of cases.
In Spain, the decisive factor is not a new biological epidemic but the postponement of motherhood for socioeconomic reasons. The mean age at first birth is around 33, fertility is among the lowest in the world (1.10 children per woman), and one in ten births is already to mothers aged 40 or over; women themselves cite lack of financial resources, difficulty reconciling work and family life, and fear of the impact on their careers as the main barriers. That is why the most effective lever is social and preventive, not merely clinical: early information about the age-related decline in fertility; measures addressing the structural causes of postponement (housing, job insecurity, work–family balance, and shared responsibility for caregiving); early reproductive assessment in primary care; honest counselling about egg freezing, without presenting it as a guarantee; and more rational, equitable public access to assisted reproduction, without overlooking the male factor. Precision reproductive medicine and genomics also open up a horizon for better characterising the causes and refining individual prognosis.