Nicotine exposure and metabolism during pregnancy among First Nations individuals in Queensland, Australia

Higher smoking rates during pregnancy are observed among First Nations peoples than non-First Nations populations in Australia. The urinary nicotine metabolite ratio (NMR), which is the ratio between the two major nicotine metabolites, total 3-hydroxycotinine (free 3-hydroxycotinine and its glucuronide conjugate) and free cotinine, indicates the nicotine metabolism rate. Previous studies, conducted in predominantly White populations, have demonstrated an increase in the rate of nicotine metabolism as gestation progresses, and suggested that increased smoking intensity may occur during this time to compensate for faster nicotine elimination. This study investigated nicotine exposure and nicotine metabolism during pregnancy in a primarily First Nations cohort. A prospective observational study was conducted on Butchulla Country in Queensland, Australia. Urine samples collected during pregnancy by 83 individuals were analysed for nicotine, 3-hydroxycotinine and cotinine. Of these, 45 individuals with urine cotinine values above threshold (> 0.36 nmol/mg creatinine) on at least one occasion during pregnancy were included in metabolism analyses. Nicotine exposure (calculated as total nicotine equivalents, the molar sum of nicotine, cotinine and 3-hydroxycotinine and their respective glucuronide conjugates) and measures of nicotine metabolism were compared across pregnancy. Regression modelling indicated that NMR increased over the course of pregnancy, while no significant change in nicotine exposure across trimesters was detected, consistent with previous literature. The findings must be interpreted with caution due to the limited number of participants and inconsistent timing of urine sample collection across the three trimesters. This research provides preliminary observations of nicotine exposure and metabolism during pregnancy in a predominantly Australian First Nations cohort.