Childbirth timing and completed family size by the mode of conception—the role of medically assisted reproduction: a population-based cohort study in Australia

BACKGROUND: With declining total fertility rates to below replacement levels amongst all high-, middle- and low-income countries, coupled with increasing use of medically assisted reproduction (MAR) treatments globally, we describe the impact of these treatments on completed family size and childbearing timing in a country with unlimited publicly funded access to MAR. METHODS: We utilised a unique longitudinal propensity score-weighted population-based birth cohort that included nulliparous mothers who gave birth after all major forms of MAR treatments (assisted reproductive technologies [ART], ovulation induction [OI], and intrauterine insemination [IUI]) and after natural conception (reference category) in Australia, 2003–2017. We followed first-time mothers over their reproductive lifespan (15–50 years). The primary outcome was completed family size (i.e., the mean cumulative number of children per mother of our cohort) and the fertility gap (i.e., adjusted difference in completed family size between MAR conceptions and the reference). FINDINGS: Our cohort includes 481,866 first-time mothers, mean follow-up of 13.8 years. ART mothers (n = 25,296) were six years older (mean age: 34.6 years) than mothers who conceived naturally (28.7 years (reference)) while OI/IUI mothers were only 2.2 years older (31.0 years) than the reference. ART mothers had up to 27% smaller completed family size (2.54 children) compared to OI/IUI mothers (2.98 children) and natural conception mothers (3.23 children). ART mothers who resided in the lower socioeconomic areas were less likely to reach a similar family size to the natural conception mothers (fertility gap of 0.83 fewer children per ART mother compared to natural conception mothers) than ART mothers who resided in the higher socioeconomic areas (0.43 fewer children). INTERPRETATION: Greater awareness of the limitations of MAR treatment to resolve childlessness and achieve desired family size is needed. Furthermore, with policymakers increasingly turning to MAR treatment as a tool to reverse declining fertility rates, their potential impact should not be overestimated. FUNDING: Australian National Health and Medical Research Council.