As a group, adolescents have worse birth outcomes than adults (Chen et al. 2007, World Health Organization 2008), but the factors that predict birth outcomes in this adolescent group are much less studied. Personality has been shown to be related to numerous health outcomes, a finding consistent across several countries and cultures (Voracek 2006, Iwasa et al. 2008, Fry & Debats 2009, Schrier et al. 2013), but few researchers have examined its associations with pregnancy and birth outcomes.
Personality is a robust, longitudinal predictor of many health outcomes. One of the most common and broad personality inventories incorporates five factors: conscientiousness (reliability, conventionality, industriousness), neuroticism (emotional stability), extraversion, openness (intellectual curiosity, appreciation for art, imagination) and agreeableness. Studies of this five-factor inventory found that higher conscientiousness is strongly related to reduced mental and physical disorders, fewer physical limitations, slower disease progression and longevity (Friedman 2000, Goodwin & Friedman 2006, O'Cleirigh et al. 2007, Jokela et al. 2013a)and has also been associated with a reduced risk of hypertension, sciatica, stroke, hernia, tuberculosis, joint problems, renal failure and mental illness (Goodwin & Friedman 2006). Reviews and meta-analyses indicate that conscientiousness, but not other personality factors, are associated with lower obesity (Jokela et al. 2013c) and diabetes risk (Jokela et al. 2013b). Neuroticism predicts worse physical health and mental health, including coronary heart disease (Jokela et al. 2013d), and worse subjective well-being (Friedman et al. 1995, Goodwin & Friedman 2006). Extraversion is associated with lower risk of some mental health issues (Goodwin & Friedman 2006) and stroke death (Jokela et al. 2013d). Centenarians score high on conscientiousness, extraversion and openness(Masui et al. 2006) and these factors have been prospectively associated with mortality (Iwasa et al. 2008, Fry & Debats 2009). Openness has also been associated with reduced metabolic risk (van Reedt Dortland et al. 2012). Cancer incidence and mortality seem largely unaffected by personality, however (Jokela et al. 2014).
Some of the reasons for these associations are clear. in general, conscientiousness is associated with a reduced likelihood of harmful health behaviours and an increased likelihood of health-promoting behaviours. The subfacets of conscientiousness, including conventionality, sense of duty and industriousness, predispose to forming intentions in line with societal values (such as health) and being able to carry them out (Bogg 2008). A meta-analysis of 194 studies concluded that conscientiousness was associated with a reduced likelihood of drug use, excessive alcohol use, unhealthy eating, risky driving, risky sex, suicide, tobacco use and violence (Bogg & Roberts 2004). They also found that many of these relationships were stronger in those <30 years (Bogg & Roberts 2004), especially in women (Kashdan et al. 2005, Hampson et al. 2006). The strongest associations are seen with drug and alcohol use, risky driving, violence and physical activity, with weaker associations (although still significant) with eating behaviours, smoking and risky sexual behaviour (Bogg & Roberts 2004, Rhodes & Smith 2006). Women with high conscientiousness are less likely to smoke during pregnancy (Maxson et al. 2012). Neuroticism is also consistently associated with less health-promoting behaviour, including sexual risk-taking and physical activity (Hoyle et al. 2000, Rhodes & Smith 2006). Extraversion tends to have mixed associations: greater physical activity (de Bruijn et al. 2005, Rhodes & Smith 2006) and wellness behaviour (Booth-Kewley & Vickers 1994), but increased likelihood of smoking, alcohol use and not getting enough sleep, demonstrated in both college students and Navy personnel (Booth-Kewley & Vickers 1994, Raynor & Levine 2009). The combination of high extraversion and low conscientiousness is also associated with alcohol use during pregnancy (Ystrom et al. 2012). Agreeableness has generally been associated with better health behaviours, including reduced sexual risk-taking (Hoyle et al. 2000), increased vegetable consumption (de Bruijn et al. 2005) and less traffic risk-taking (Booth-Kewley & Vickers 1994). These associations are quite stable: personality in childhood predicts adult health behaviours, even after 40 years (Hampson et al. 2006).
Personality also relates to healthcare seeking and compliance. Some studies have found that adherence to a treatment regimen, associated with conscientiousness, is more strongly associated with health than treatment assignment (active vs. placebo) (Friedman 2008). Diabetic children and their mothers who demonstrated high conscientiousness, low neuroticism and high agreeableness had better glycaemic control (Vollrath et al. 2007). Conscientiousness is also associated with better disease progression in people with HIV, partly due to medication adherence (O'Cleirigh et al. 2007). Neuroticism can be characterized by pessimism and lack of adherence to treatment regimens, or obsessive adherence and vigilance (Friedman 2008). For instance, neuroticism has been associated with use of anxiolytics and antidepressants during pregnancy, but also with quitting smoking during pregnancy (Ystrom et al. 2012). Neuroticism can also affect how symptoms are presented to clinicians and the treatment patients receive (Ellington & Wiebe 1999). However, personality, particularly conscientiousness, has been shown to be related to outcomes such as overall health status and mortality, beyond the known associations with behaviour and healthcare compliance (Friedman et al. 1995, Hampson et al. 2007, Lodi-Smith et al. 2010).
Despite the numerous associations seen with health behaviours and other health outcomes, personality has not been extensively studied with respect to pregnancy. Only a handful of pregnancy-related studies on a variety of topics can be mentioned. Higher extraversion, openness, conscientiousness and emotional stability are associated with women having more children (Jokela et al. 2011). Unplanned pregnancy is associated with higher neuroticism and lower agreeableness and conscientiousness (Bouchard 2005, Berg et al. 2013). Neuroticism has been associated with more somatic symptoms during pregnancy, while agreeableness is associated with fewer symptoms (Puente et al. 2011). The only study of birth outcomes that we are aware of found that higher neuroticism was associated with foetal growth restriction and smaller head circumference; extraversion was not associated with birth outcomes, nor was there an association between personality and preterm birth (Chatzi et al. 2013). Another study found that women with higher neuroticism and introversion were more likely to have Caesarean deliveries and labour/birth complications, but found no associations with agreeableness or conscientiousness (Johnston & Brown 2013). Mothers who score high on conscientiousness and extraversion and low on neuroticism are more likely to breastfeed (Brown 2014).