Maternal ACEs were common in this study, and significantly associated with illicit drug use in this community-based, middle to high-income sample of pregnant women. The proportion of the sample that reported illicit drug use while pregnant was 3.1%, which is comparable to other studies which show that 1% to 6% of women in community-based samples report illicit drug use in pregnancy (1–7). The frequency of ACEs reported in this study were comparable to national US research collected within a similar time frame. Specifically, 62% of women in the present study reported at least one ACE, and a mean ACE score of 1.5. A 2011-2014 surveillance study across 23 US states similarly documented that 62% of adults reported at least one ACE, and a mean ACE score of 1.7 (51). The US survey found childhood emotional, physical and sexual abuse was reported by 34%, 18%, and 16% of American women; respectively (51). In the present Canadian sample, childhood emotional, physical and sexual abuse was reported by 36%, 17%, and 13% of women; respectively. Exposure to household dysfunction in the present sample was also similar to US estimates, with parental separation/divorce and parental substance use reported by 34% and 18% of American women, compared to 23% and 21% of Canadian women in this study (51).
In the present study, an ACE score of four or more was moderately associated with illicit drug use in pregnancy (odds ratio of 3.7). This finding differs from Chung et al. (2010) who found four or more ACEs was strongly associated with illicit drug use in pregnancy (odds ratio above 7) among women in the US (38). A key reason for this difference may the average socioeconomic status between the samples. In the US study, the sample largely consisted of young (mean age: 24 years), single (75% unmarried) women with low educational attainment (18% had completed university or college) and low income (38). In the present study, the sample largely consisted of mature (mean age: 31 years), married (90%), well educated (81% had completed university or college) women with middle to high household incomes. It may be that the higher average SES of women in the present sample provided some level of protection against the impacts of maternal ACEs on drug use in pregnancy, as compared to women examined by Chung and colleagues. For example, higher SES may have provided women in our Canadian sample with greater access to resources that could address the mental health impacts of ACEs on their well-being or problematic drug use before and during their pregnancy. We note that there are only a small number of effective therapies for substance use in pregnancy (52). These primarily involve behavioural counselling, the costs of which are seldom covered by government health insurance programs, and require significant personal resources to take part in (52). Most women in our sample also had a post-secondary degree and thus the sample may have been more aware, on average, about the impacts that ACEs could have on their well-being and/or the impacts that illicit drug use could have on their pregnancy.
Yet, it is also important to note that the elevated SES of the present sample did not eliminate the impact of ACEs on illicit drug use in pregnancy. The association observed in our sample was statistically significant and moderate in strength, suggesting that even among more affluent populations, maternal ACEs are an important risk factor for illicit drug use among pregnant women. Mediators of this association may be similar to those observed in men and women in general population studies. It is well documented that exposure to ACEs may result in psychological, behavioral and neurobiological adaptations that promote short-term survival for a child in their environment, while conferring longer-term vulnerability across a wide range of health-risk behaviors, including drug use (53). ACEs result in threat-related social information processing biases, heightened emotional reactivity, difficulties with emotional regulation, and blunted reward responsivity which can drive individuals toward more intense reward-seeking in order to successfully alleviate these adverse states (54–58). Entering into pregnancy with an elevated ACE score may heighten these impacts given it is an emotionally vulnerable time for women. From a multigenerational perspective, women with elevated ACE scores may also receive less social support from their parents during pregnancy relative to other women, or may continue to experience emotional abuse from their parents as adults, which could influence or exacerbate illicit drug use in pregnancy. It is recommended that future studies examine these and other potential mediators of the associations observed in this study in large samples of pregnant women in order to accommodate such analyses. The findings of this study do not suggest that a large percentage of women with an elevated ACE score will use illicit drugs in pregnancy. The overall percentage of women who reported illicit drug use while pregnant remained small, regardless of maternal ACE exposure. Indeed, even among women with 4 or more ACEs, 93% reported they did not use illicit drugs during their pregnancy.
Building on the work of Hall & van Teijlingen (2006), more qualitative studies with the small numbers of pregnant women who use illicit drugs is also recommended to understand their needs and inform prevention efforts (59). The results of this study suggest these qualitative samples should include community-based women from across the socioeconomic spectrum to ensure a full understanding of the drivers of illicit drug use in pregnancy across different populations.
Limitations
The associations documented in this observational study do not imply causation. Data collected on maternal ACEs and illicit drug use in pregnancy were based on self-report. While retrospective reports of major, easily defined ACEs have acceptable psychometric properties (60,61), illicit drug use in pregnancy is frequently underreported (5). We note that underreporting is particularly amplified in jurisdictions that have laws that penalize women for prenatal drug use (4–6), which was not the case for the present sample. Data were collected in a Canadian province that does not have laws that penalize women for prenatal drug use. Underreporting due to social desirability bias is also a concern (62). To reduce this data were collected by mailed surveys rather than face-to-face interviews, women were reminded their responses were confidential, and returned surveys included only a participant’s ID (63,64). Despite these efforts, the likely underreporting of illicit drug use in pregnancy remains a limitation of this study. That said, the literature does not suggest differential reporting of substance use in pregnancy by maternal ACE score. Thus, we expect the misclassification of some pregnant women who had used illicit drugs into the non-drug use group was non-differential and would not bias the associations observed in the direction of a Type 1 error (65). We note there was attrition over the course of the study, with approximately 70% of participants returning all survey packages mailed to them, and 58% of women completing all questions relevant to this secondary analysis of the data.
English fluency was required to participate. Census data indicate 92% of Alberta adults across all ages were fluent in English during the period in which data were collected (66). Given English fluency is higher in younger populations, and no participants exceeded the age of 45 in this study, we do not expect English fluency significantly impacted participant recruitment, but note it as a possible limitation.
4.1 Conclusions
Maternal ACEs were common and associated with a moderate increase in the odds of illicit drug use among community-based pregnant women with middle to high socioeconomic status in Canada. Illicit drug use in pregnancy is a critical public health concern linked with a variety of harmful maternal and fetal consequences. The present findings speak to the public health significance of maternal ACEs on illicit drug use in pregnancy, and the need for increased resources to support women of childbearing age who have experienced childhood adversity.