In order to study personality changes in first pregnancy and lactation, two groups of women (n = 161, mean age 26.8 years) completed the self-report inventory Karolinska Scales of Personality and a scale for emotional dependency during pregnancy and 3 or 6 months after delivery. The results were within normal limits when compared with the normative values. Analysis of variance showed that the subscales Muscular Tension, Somatic Anxiety, and Monotony Avoidance diminished significantly from pregnancy and to the test periods after delivery (all p values < 0.01). Impulsiveness showed the same trend (p = 0.1). The women who had breastfed for at least 8 weeks (91%) differed significantly from those who had not. They had lower scores on the Somatic Anxiety (p = 0.006), Muscular Tension (p = 0.003), Monotony Avoidance (p = 0.039), Suspicion (p = 0.03), Social Desirability (p = 0.045) and the Impulsiveness scale (p = 0.078) and higher scores on the Socialization scale (p = 0.001). Thus, we conclude that most personality traits are stable during first pregnancy and lactation, but some significant changes occur toward a lifestyle interpreted as more relaxed and tolerant to monotony.