Personality traits in women 4 days postpartum and their correlation with plasma levels of oxytocin and prolactin

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Abstract
The aim of the present investigation was to explore whether the personality characteristics of women who have recently given birth differ from those of a control group of similar aged women and if so, whether such deviations are related to the pregnancy- and lactation-associated hormones oxytocin and prolactin which in animal experiments have been shown to play a role in maternal behavior. Thereforethe Karolinska Scales of Personality (KSP) were used in 50 women 4 days postpartum and in addition 18 blood samples were drawn in connection with breastfeeding. Oxytocin and prolactin levels were measured by radioimmunoassay. The women investigated scored lower in Muscular Tension (p < 0.05), in Monotony Avoidance (p < 0.001) and Psychasthenia (p < 0.01) and higher in Social Desirability (p < 0.001) than a reference material. Plasma levels of oxytocin and prolactin rose as expected in response to breastfeeding. When the average prolactin and oxytocin levels obtained at the 18 different timepoints of each woman were correlated with the scores obtained in the various KSP items, some significant relationships were found. Significant positive correlations were found between prolactin and the KSP dimensions Social Desirability and Inhibited Aggression and negative correlations with Psychasthenia. Significant inverse relationships between oxytocin and several Anxiety and Aggression variables, Guilt in particular, were also found. Correlations with oxytocin and prolactin levels were as a rule particularly clear in samples collected during breastfeeding. The data obtained are discussed from a biological point of view in relation to the specific 'maternal behavior' described in other mammals. It is suggested that subtle psychological and behavioral changes occur in women during motherhood and that these changes may in part be related to prolactin and oxytocin.