The interaction of pregnancy, substance use and mental illness on birthing outcomes in Australia

Background: this study aimed to (1) assess the prevalence, and demographic features of women with a history of mental illness during pregnancy and childbirth, (2) investigate maternal and perinatal outcomes in relation to mental illness and substance use, and (3) determine the effects of maternal characteristics, history of mental illness and substance use on birth outcomes. Methods: the records of 22,193 pregnant women who gave birth at one tertiary level health service comprising three maternity settings in Victoria, Australia from 2009 to 2011 were reviewed. Univariate comparisons for socio-demographic and birthing outcome variables by substance use and mental illness category were performed. A multivariable logistic regression model was developed to examine the effects of maternal characteristics on birth outcomes. Results: mental illness was recorded for 1.08/1,000 delivery hospitalisations. Mothers with a history of mental illness had a significantly higher proportion of babies born with low birth weight (OR = 1.85, 95% CI 1.64 -2.09) and low Apgar 1 scores < 7 (OR = 1.47, 95% CI 1.26 -1.70). Differences in health behaviours were also noted between the two groups. Babies born to women with an illicit and poly substance use history reported an average birth weight at 2,951 (SD 777) grams compared to birth weight of approximately 3,300 g of smoking and alcohol user groups, as well as shorter gestational age and lower birth weight. There was a statistically significant interaction between the effects of mental illness and substance use on birth weight. This interaction effect was not significant for gestational age. Logistic regression showed the strongest predictor of reporting a premature birth and low birth weight was using substances, recording an odds ratio of 1.95 (95% CI 1.50-2.53) and 2.73 (95% CI 2.15-3.47) respectively. Conclusions: mental health history should be highlighted as being a common morbidity and the increased risk of poorer birth outcomes especially when the women were also using substances, alcohol or tobacco should be acknowledged by the health practitioners.