50 years of comprehensive state-wide data on pregnancy termination in South Australia: a retrospective, population-based, cohort study.

Background: Termination of pregnancy is a common procedure, accessed globally, irrespective of logistical and legal barriers. We aimed to document changes in procedural characteristics and demographic factors over time in South Australia, as well as to examine how key sociodemographic variables affect gestational age at pregnancy termination.

Methods: South Australian legislation has required mandatory collection of data related to pregnancy termination since 1970. We conducted a retrospective population-based cohort study of all pregnancy terminations in the state from 1970 to 2020. The primary outcome was gestational age at termination of pregnancy. Linear regression was used to examine socioeconomic characteristics that could confer disadvantage in access to pregnancy termination, with postcodes coded according to the 2016 Australian Statistical Geographical Classification-Remote Area system and the Index of Relative Socio-Economic Advantage and Disadvantage (IRSAD) from the Australian Bureau of Statistics 2018.

Findings: Between Jan 1, 1970, and Dec 31, 2020, 225 440 pregnancy terminations were performed at a median of 8 weeks' gestation (IQR 7-10). Most pregnant individuals (median age 24 years [IQR 20-31]) resided in urban areas (n=166 311 [77·9%]) and received surgical pregnancy termination (n=287 345 [78·4%]). Major complication rates remained low over time; however, major complications occurred more frequently at higher gestational ages. Gestational age at pregnancy termination decreased over time (from 9 weeks [IQR 8-11] in years 1970-75 to 7 weeks [6-9] in years 2016-20) and was strongly correlated with being a teenager (ie, aged <20 years), rurality, and IRSAD score, with individuals at greater levels of socioeconomic disadvantage undergoing pregnancy termination at consistently higher gestational ages.

Interpretation: Over time, there have been many changes in the demographics of women and the method used for pregnancy termination. Even in a high-income country with legal and publicly funded access to pregnancy termination, there are significant differences in the gestational age at which pregnancy termination occurs, which vary with socioeconomic disadvantage. Understanding changes in the demographics of those undergoing this procedure and the influence of various indicators of socioeconomic disadvantage is vital for optimal service provision.

Funding: None.