Recent studies have tried to explore what we can do to manage and prevent a potential psychiatric disorder developing in future generations. These studies highlight that a variety of early life risk factors can influence common mental disorders, such as depression (Brown et al, 2000) and schizophrenia (Khashan et al, 2008). These early life risk factors include prenatal stress, social support, maternal anxiety, childhood trauma and temperament (Rice et al, 2007).
Could these risk factors also contribute to the likelihood of being diagnosed with a personality disorder in the future? Do early precautions need to be taken for expectant mothers? Currently, there is very little supportive literature to identify if prenatal stress exposure is related to a rise in the likelihood of developing a personality disorder.
Personality disorders can have a significant psychosocial impact, resulting in functional impairment, a rise in suicide rates, and large financial costs arising from both direct treatment costs and use of long-term health services (Chanen et al. 2007). However, it is difficult to identify those who could be at risk of developing a personality disorder. There is no tool available to predict the possibility of a diagnosis, and early risk factors, such as childhood trauma or loss of a parent, are often only measured retrospectively.
Brannigan et al (2019) conducted a study to investigate if exposure to any level of mental stress during the gestational period could be a potential risk factor for an increased likelihood of the offspring developing a personality disorder.
The authors collected data from the Helsinki Temperament Cohort, in which all births between 1st July 1975 and 30th June 1976 in the greater Helsinki area were recorded. Their main focus was the subsample of 3,626 mothers (from the prospective birth cohort of 6,468), who completed regular health and well-being assessments during pregnancy. These assessments were done during monthly antenatal clinic appointments, and the expectant mothers were asked about any form of subjective prenatal stress during the preceding month. The questionnaire also addressed their physical health and wellbeing during the previous month, ascertaining for example how often they had smoked cigarettes.
The primary outcome of interest was obtained through the linkage between the Finnish National Population Register (FNPR) and the Finnish Hospital Discharge Register (FHDR). The data was collected from FHDR in 2005, and the mean sample age was 30 years old. The diagnoses were recorded in the register, depending on the date of the diagnosis, using the ICD-8 (1967), ICD-9 (1978) or ICD-10 (1992).
The authors noted that certain confounders can be found to influence prenatal stress during the pregnancy and potentially increase the risk of offspring developing psychiatric disorders. Therefore, the following data was also collected:
- Maternal and paternal psychiatric history from the FDHR
- Total prenatal questionnaires returned
- Maternal smoking during pregnancy
- Maternal report of depression during pregnancy
- Other psychiatric disorders.
The confounders were added to the outcome in a stepwise fashion, in order to capture if there was any impact in addition to prenatal stress on the results. The final outcome was adjusted after the confounders were controlled for, to see if exposure to self-reported mental stress during the gestation period can be independently associated with the increased odds of the offspring developing a personality disorder.
The authors identified 40 individuals with personality disorders within 3,626 members of the cohort. Of those 40, 31 (77.5%) had at least one comorbid diagnosis of either a psychotic, depressive or anxiety disorder.
Exposure to mental stress during gestation led to a 3-fold increase in the odds of being diagnosed with a personality disorder, compared to those unexposed to stress (odds ratio 3.28, p<0.05). Furthermore, exposure to severe prenatal stress led to a 9-fold increase in the odds of a personality disorder diagnosis in the offspring (odds ratio 9.53, p<0.05)
Despite controlling the confounders by adjusting for the diagnoses of a depressive, anxiety or a psychotic disorder, the final data analysis showed that the increase in odds persisted. This suggests that the effect of prenatal stress is independent of comorbid psychiatric disorders.
The authors acknowledge that the specific mechanism of how prenatal stress increases the risk of personality disorder is not clear. They point out, however, that those mothers who reported experiencing ‘severe stress’ were at far greater risk of their offspring developing personality disorder than those experiencing ‘moderate stress’. This suggests that the mothers own subjective rating of the prenatal stress may impact on the likelihood of their offspring developing personality disorder.
The authors noted that previous studies have examined brain scans which reveal that those diagnosed with a personality disorder have significantly reduced volumes of grey matter throughout particular brain regions, including the limbic system, the frontal lobe, left orbitofrontal cortex and right anterior cingulate cortex (Driessen et al, 2000). Moreover, studies have found that prenatal stress can lead to reduced volumes of grey matter in middle childhood in brain regions such as pre-frontal cortex, premotor cortex, medial temporal lobe, lateral temporal cortex and postcentral gyrus and cerebellum (Buss et al, 2010). Combined, these findings suggest that prenatal stress could lead to reduced grey matter in offspring’s developing brains, which in turn may result in development of personality disorder.
There are also a variety of psychosocial factors that could influence the relationship between prenatal stress and the later development of personality disorder in the exposed offspring. For instance, prenatal stress may result in childhood maltreatment which, in turn, may lead to later psychopathology, including the development of personality disorder. A cohort study by Plant et al (2017) found that maternal childhood maltreatment independently predicts the offspring’s emotional and behavioural difficulties in preadolescence. This suggests that prenatal stress may affect the child-parent parenting style, which in turn results in the child’s developing psychopathology.
Strengths and limitations
This is the first study to examine the linkage between maternal stress during pregnancy and the possibility of the offspring receiving a diagnosis of personality disorder in the future.
This study has many strengths, including the separation of the effects of prenatal stress and depression, whereas in previous studies these have been considered as one concept. The authors felt that their results were promising, showing a significant independent association between prenatal stress and the later diagnosis of personality disorder in the offspring. They advised in their study:
We encourage future studies to separate these exposures to shed light on mechanisms by which stress, depression and anxiety during pregnancy later affect the mental health of the offspring.
The outcome data were extracted from FHDR, which has been found to have excellent diagnostic validity, compared to the DSM.
However, there were limitations to the study, as follows:
- This study may under-represent the number of personality disorder patients in the cohort sample, as it included only those who required admission to hospital (severe cases). We do not know, regarding personality disorder patients in the community, if their mothers were exposed to similar stress indicators.
- There is the possibility that the associations could have arisen through the mother and offspring sharing some of their genome. By using genetically sensitive designs, we could test and identify the true effects of prenatal risk factors independent of the relationship between maternal and offspring genomes.
- This study did not measure other confounders, such as maternal education, familial socio-economic status, and physical and sexual abuse, which may have impacted on the mental stress of the expectant mothers. This impact is likely to have lasted throughout the gestational period, making it difficult to isolate these confounders and separate it from the results presented here.
- It has previously been suggested that stress exposure at different trimesters of gestational period can have different impacts on the likelihood of developing a major affective disorder (Brown et al, 2000). It would be useful to identify if a similar association exists between prenatal stress exposure during different trimesters of pregnancy and personality disorders.
- The authors declared that they were unable to split personality disorders into individual disorder or disorder clusters. However, they note that most people meeting criteria of one personality disorder will meet criteria for the second (Widiger et al, 1989), meaning the results should be true for multiple personality disorder diagnoses.
Implications for practice
The NHS England is investing £36.5 million into perinatal mental health services, as part of a five-year programme. This will allow new and expectant mothers to easily access services in the community, highlighting the importance of close monitoring during the postnatal period. However, Brannigan et al’s (2019) study has shown why it is also important to invest during the pre-natal period. The impact of prenatal stress can increase the likelihood of the offspring developing a mental illness, just as the impact of postnatal stress can (Rees et al, 2018).
Overall, this study acknowledges the need for psychological and psychosocial interventions around treating maternal depression (particularly during pregnancy). By offering safeguarding against adverse childhood experiences to mothers with traumatic childhood histories, it could provide protection for the next generation’s psychopathology.
It is important to be cautious with this study’s findings, as many of the stress indicators during the antenatal period could continue to persist during the postnatal period, such as housing situations and finances. By using designs that separate prenatal and postnatal effects we can identify when it is required to intervene and implicate policy and practice (Swanson et al., 2008). Additionally, the stress factor could possibly continue into the postnatal period, potentially affecting the parent-child relationship, parenting style and comfort, all of which have an impact on the child’s neurodevelopment. Studies have reviewed child-parent attachment and later diagnosis of borderline personality disorder, suggesting that bipolar personality patients were more likely to have preoccupied/unresolved attachment to their parents (Levy et al, 2005).
More research is needed to explore the methodologies of available studies, and identify the at-risk parents and new-borns, so that appropriate opportunities are offered to intervene and prevent. Consequently, this would improve understanding of the effects of prenatal stress on the outcome of the offspring’s mental health.
This study could cause additional pressure for expectant mothers, as it provides an unrealistic approach for a stress-free pregnancy. Bearing an unborn child automatically alters several aspects of the expectant mother’s life. The adjustment can be challenging, and it might be helpful to invest in practical support that would reduce the subjectivity of the expectant mothers’ stress levels.
Statement of interests
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