Abstract
Background: Pregnancy rates amongst users of combined oral contraceptives (COCs) in Aotearoa New Zealand (Aotearoa/NZ) are unknown. Filling this gap aims to help guide future research and initiatives for achieving equitable contraceptive services in Aotearoa/NZ.
Objective: To estimate the rate of pregnancy among users of COCs in Aotearoa/NZ in 2019, and explore correlates of pregnancy rate across sociodemographic and geographic factors.
Methods: This retrospective cohort study used whole-of-population data from the Integrated Data Infrastructure, a research database containing deidentified routinely collected government data. Users of COCs were identified using pharmaceutical dispensing data, and pregnancy events were identified in maternity and hospital discharge datasets. Pregnancy events were included if they were estimated to have been conceived during a period of COC use. Observed pregnancy rates were calculated for the entire study population, new and established users, and sociodemographic and geographic subgroups. Rates were analysed using Poisson regression models to produce comparative risk ratios and 95% CIs that were adjusted for covariates.
Results: A pregnancy rate of 3.50 per 100 person-years of COC use was identified from a cohort of 208 197 individuals using COCs in Aotearoa/NZ in 2019. There was significant variation in pregnancy rates by several key sociodemographic and geographic factors including by whether a user was new/restarting or established (reference) on COCs (adjusted risk ratio 1.28, 95% CI 1.19 to 1.37), or lived in a rural or urban (reference) area (adjusted risk ratio 1.32, 95% CI 1.21 to 1.44). There were also significant differences in pregnancy rate by age group, ethnicity, parity, highest qualification, household income, and neighbourhood deprivation.
Conclusions: The estimated pregnancy rate among users of COCs in Aotearoa/NZ is comparable to international findings. Sociodemographic and geographic variation in pregnancy rates may be explained by inconsistent pill use, access barriers, contraceptive failure, and early discontinuation of COCs with intended pregnancy conception. An opportunity remains for further research to fully understand the drivers of such variation. Nevertheless, these findings will inform family planning services, clinical practice, and public health policy. Furthermore, they have implications for whether healthcare services are providing equitable contraceptive care and meeting the needs of contraceptive users.