Do anxious mothers pass their stress on to their babies?
This post was co-authored by Margarita Kanevski and Sinead Rhodes.
In amidst of a global pandemic with many existing and expectant mothers already finding themselves in a heightened state of uncertainty, this recent headline by The Daily Mail would itself be more than enough to scar anyone for life. Upon a closer look, however, this attention-grabbing headline certainly calls for scrutiny in the context of the science behind it.
What did the actually study do?
The study was recently presented as an abstract at the European College of Neuropsychopharmacology congress. Researchers administered the famous Still Face Paradigm to 50 mothers and their three-month-old babies. During this paradigm mothers first interacted with their infant in a playful and engaging manner (playful phase) following which they were instructed to stare at their infant and remain still (stressful phase). The stressful phase, during which the mother acts distant, has been consistently shown to invoke signs of distress in children. Following the stressful phase, mothers were asked to resume engaging playfully with their child. To measure stress, researchers monitored heart rate activity of infants and their mothers throughout the task (where higher heart rates reflected increased stress levels).
Mothers were interviewed using the Diagnostic Interview for Mental Disorders to assess if they met criteria for an affective disorder, also known as a psychiatric/mood disorder. In total, 20 of the mothers met criteria for one or more affective disorders and were included in the experimental group (a group with a condition of interest). The remaining 30 of the mothers did not meet criteria for an affective disorder and therefore formed the control group (a group without a condition of interest). Researchers compared the heart rates of infants and mothers across these two groups. Additionally, the researchers asked mothers to rate infants’ general temperament including things like smiling, laughter, fear, and distress.
Results showed that babies of mothers with one or more affective disorders had higher heart rates during the stressful phase of the experiment, than babies in the control condition. The babies of mothers with an affective disorder were also rated by their mothers as being more negative in their general temperament. Importantly, researchers accounted for other important factors that could have been driving this difference between the groups, including maternal age at time of birth, income, and children’s birthweight. The authors concluded that babies with mothers suffering from an affective disorder struggle to deal with stressful situations.
How well did the media cover the findings?
The headline asserts that anxious mothers ‘pass’ on their stress to their babies. To infer that mothers ‘pass’ any traits to their offspring would require a complex examination of mother-child genetics which was not done in this specific study. Based on this, we cannot infer that mothers ‘pass’ on their stress to their infants. Notably, mothers in the control group (without an affective disorder) were found to have higher heart rates across all three phases of the study, which would actually suggest that these mothers were experiencing more stress during the experiment than mothers with affective disorders.
The headline also misleads the reader to infer that mothers were exclusively anxious. Rather, mothers were assessed using the Diagnostic Interview for Mental Disorders for affective disorders, which covers other debilitating conditions such as bipolar disorder and major depressive disorder. The study abstract did not provide a breakdown of which affective disorders mothers in the experimental group met criteria for the most. As such, asserting that findings relate to anxious mothers is misleading and is especially concerning given that postpartum anxiety or, in other words, excessive worry following giving birth, has been estimated to affect 13 to 40% of mothers, making it relatively common. The article goes on to state that having an anxious or depressed mother can scar children for life. However, the study did not follow infants up over time and so no conclusions can be drawn regarding their well-being across the lifespan.
Other things to keep in mind
The first important point to consider is that the findings of the study are preliminary. This means that the work around the experiment is likely still ongoing and these are only the initial emerging findings. Indeed, the researchers themselves state that further work with a larger number of participants will be required before any final conclusions can be drawn.
Second, for findings of a study to be deemed as consequential and not occurring simply by chance, scientists typically rely on a statistical significance value (known as a p-value) being smaller than 0.05. If we look at the reported significance values for the group difference between the heart rates of infants across the two groups, these fall marginally just below this threshold (0.048 to be specific). This, coupled with the small sample size, challenges any conclusions that can be made based on the findings of this single study. Replication of this research, particularly by other independent research groups, is important before we can generalise the findings to mothers and infants in general.
Lastly, the study has not yet been peer-reviewed. It was presented at a conference and picked up by the media rather than being in a final peer reviewed publication. Peer review refers to the assessment of scientific work by other experts in the field and represents a critical aspect of validation of the quality of any research. Until this study is finalised and peer reviewed, we must be careful about interpreting its findings.
Useful links
https://www.nhs.uk/conditions/post-natal-depression/
researchtheheadlines.org 