Shifting the reproductive window: The contribution of ART and egg donation to fertility rates in the UK.

Delayed childbearing in advanced economies has increased reliance on assisted reproductive technologies (ART). Yet, how ART and especially donor egg treatments contribute to population-level fertility rates remains under-studied. Analysing all ART treatments in the UK (1991-2018), we document rising ART usage: ART-conceived births contributed 3.0 per cent to the total fertility rate in 2018 and 14.9 per cent to fertility rates among women aged 45-50. ART success rates show a clear age-related decline when using women's own eggs but remain consistent across age groups when using donor eggs. Consequently, from age 43 onwards, ART-conceived births result predominantly from donor egg treatments. Our findings indicate that fertility recuperation at advanced ages is unlikely to succeed with ART using a patient's own eggs; egg donation and egg freezing appear indispensable for supporting fertility at advanced ages with ART. This has significant implications for public health communication, as this fact is not widely known.