The modest impact of assisted reproductive technology on the second birth: insights from a population-based study in Lombardy, Northern Italy

Background: In the field of assisted reproductive technology (ART), family rate is a neglected but emerging issue. The aim of the study was to investigate the epidemiological impact of ART on the second birth during the period 2007-2020 in Lombardy, Northern Italy. Methods: We conducted a population-based study using administrative data from regional healthcare databases of Lombardy including first and second births occurred from 2007 to 2020. The proportion of deliveries after ART was calculated separately among first and second births. The probability of undergoing ART to achieve second birth compared to first one was estimated computing odds ratio (OR), crude and adjusted for maternal age, education, and nationality. We also assessed changes with age and calendar period.Results: We obtained a cohort including 553,190 first births and 317,976 second births. The proportion of ART babies among first and second births was 4.3% and 1.0% respectively (p < 0.001). The probability of undergoing ART to achieve second birth compared to first one, adjusted for age, education, and nationality, was 0.14 (95% CI: 0.13-0.15). The proportion of deliveries after ART increased with maternal age and along the calendar period but remained always markedly higher among first births rather than among second births.Conclusion: ART played a significantly lower role in the determinism of the conception of a second birth in comparison to the conception of a first one.