Fertility rates among adolescents have decreased substantially in recent years, yet fertility rates among adolescent girls with mental illness have not been studied. We examined temporal trends in fertility rates among adolescent girls with major mental illness.
We conducted a repeated annual cross-sectional study of fertility rates among girls aged 15 to 19 years in Ontario, Canada (1999–2009). Girls with major mental illness were identified through administrative health data indicating the presence of a psychotic, bipolar, or major depressive disorder within 5 years preceding pregnancy (60 228 person-years). The remaining girls were classified into the comparison group (4 496 317 person-years). The age-specific fertility rate (number of live births per 1000 girls) was calculated annually and by using 3-year moving averages for both groups.
The incidence of births to girls with major mental illness was 1 in 25. The age-specific fertility rate for girls with major mental illness was 44.9 per 1000 (95% confidence interval [CI]: 43.3–46.7) compared with 15.2 per 1000 (95% CI: 15.1–15.3) in unaffected girls (rate ratio: 2.95; 95% CI: 2.84–3.07). Over time, girls with major mental illness had a smaller reduction in fertility rate (relative rate: 0.86; 95% CI: 0.78–0.96) than did unaffected girls (relative rate: 0.78; 95% CI: 0.76–0.79).
These results have key clinical and public policy implications. Our findings highlight the importance of considering major mental illness in the design and implementation of pregnancy prevention programs as well as in targeted antenatal and postnatal programs to ensure maternal and child well-being.
Comments
Response to: Lynch, D. Is the age-specific fertility rate of adolescents really higher than that of other adolescents or is bias at play?
In response to our article: "Fertility rate trends among adolescent girls with major mental illness: a population-based study"(1), Dr. Lynch requests two key, related methodological clarifications that are important to the interpretation of our results. First, there is a question of whether it would be better to focus only on primiparous teenagers to truly explore the relationship between mental illness and adolescent pregnancy because of a medical surveillance bias where multiparous adolescents are more likely to be involved with the health care system and therefore more likely to receive a mental health diagnosis. Second, there is a question of whether the confidence intervals could be inappropriately narrow because of failure to account for dependency in the analysis.
We believe that our analytic approach was able to provide a more comprehensive picture of the relationship between major mental illness and pregnancy than if we had restricted the sample only to nulliparous teens, and that we were able to deal with the issue of clustering as well as possible within the constraints of an observational study using health administrative data. We accounted for multiparity in multivariable analyses as an important predictive factor, using generalized estimating equations (GEE) to deal with clustering (or dependency) in the analysis. In this analysis, we found that major mental illness was independently associated with adolescent pregnancy, even after accounting for multiparity. When observing the difference between the unadjusted estimate and the adjusted estimates (Table 2), one can see that adjustment for multiparity did slightly attenuate the independent risk of major mental illness - reflecting the fact that multiparous adolescents do tend to have higher rates of preconception mental illness than nulliparous teens. If we had focused only on nulliparous teenagers, this nuance might have been missed.
(1)Simone N. Vigod, Cindy Lee Dennis Paul A. Kurdyak, John Cairney, Astrid Guttmann and Valerie H. Taylor. Fertility Rate Trends Among Adolescent Girls With Major Mental Illness: A Population-Based Study. Pediatrics 2014; 133:3 e585-e591
Conflict of Interest:
None declared
Is the age-specific fertility rate of adolescents with mental illness really higher than that of other adolescents or is bias at play?
I read with interest the authors' paper examining the association between mental illness status and fertility among adolescent girls in Ontario, Canada from 1999-2009. While the authors are to be commended for their innovative use of administrative health data to address such a novel question, their methodology calls into question the validity of their findings.
First, in examining the data provided, one notes in Table 2 the apparent strong association between parity and subsequent fertility. Specifically, previously delivering a live born infant was associated with a 13.5 to 15.8-fold increase in having a subsequent live birth during the study period. This raises the question of the potential for medical surveillance bias, that is that since pregnancy is associated with an increased frequency of contact with the healthcare system that perhaps adolescent girls with a previous pregnancy were more likely to have been diagnosed with a mental illness than other girls. One way that the authors could address this concern would be to repeat their analyses, but restrict their population to only nulliparous adolescent girls to see if the same pattern is observed.
Secondly, the authors did not address how they dealt with the issue of dependency in their analyses. For instance, since some of the adolescents were parous in their dataset, some girls are likely to have been in the dataset twice since it spanned a 10-year period. Since in some analyses the data from all years were combined, failure to adjust for the multiple births per adolescent would result in confidence intervals that are inappropriately narrow.
Further clarification of the above-mentioned methodological concerns would assist the reader in better interpreting the findings of this groundbreaking study.
Conflict of Interest:
None declared