PURPOSE OF THE RESEARCH Tobacco smoking and alcohol consumption during pregnancy can cause life-limiting and life-threatening complications for women and children. Yet knowledge on differences in smoking and alcohol consumption across the pregnancy period is limited. This study compared smoking and alcohol use in early (<20 weeks) and late (≥20 weeks) pregnancy using routinely collected administrative perinatal data from a state-representative cohort of women in Queensland, Australia.

STUDY DESIGN Cross-sectional study using aggregate statewide data from the 2022-2023 Queensland Perinatal Data Collection.

PRINCIPAL RESULTS The sample comprised 57,757 women. Smoking prevalence decreased from 10.7 % in early pregnancy to 7.9 % in late pregnancy (absolute risk reduction [ARR] = 2.8 %, 95 %CI 2.5-3.1 %). Alcohol consumption decreased from 5.8 % to 0.7 % over the same period (ARR = 5.1 %, 95 %CI 4.9-5.3 %). Women who were single, received limited antenatal care, had late commencement of antenatal care (≥14 weeks gestation), or mental health conditions, were at higher risk of smoking and alcohol consumption in early and late pregnancy.

MAJOR CONCLUSIONS The results highlight that interventions targeting alcohol use should be delivered pre-conception and during early pregnancy, whereas smoking interventions should span the entire trajectory, as these behaviours are less likely to change overtime. Results also highlight the characteristics of pregnant women who, along with their families, may benefit from improved antenatal care and social support. To address patterns of alcohol and tobacco smoking effectively, care models must be comprehensive, accessible, and tailored to the needs of underserved populations with substance use challenges.