Maternal parity and perinatal cortisol adaptation: The role of pregnancy-specific distress and implications for postpartum mood.

Introduction: Compared to women who have given birth before (i.e., multiparas), those giving birth for the first time (i.e., primiparas) show higher cortisol levels. Psychological factors may play a role; hypothalamic-pituitary-adrenal activation is a well-described stress response. Primiparity also predicts greater risk for postpartum depression, which may be related to greater correspondence between cortisol and mood following prenatal cortisol elevations. The current study examined associations among parity, perinatal cortisol adaptation, pregnancy-specific distress, and postpartum mood.

Methods: This longitudinal study assayed serum cortisol levels among 137 women at early, mid-, and late pregnancy and postpartum. Pregnancy-specific distress and depressive symptoms were assessed. Maternal age, race, body mass index, sleep quality, depressive symptoms, and sampling time of day were statistically controlled.

Results: Primiparous women showed higher cortisol levels than multiparous women during mid- (χ = 11.8, p < 0.01) and late pregnancy (χ = 18.9, p < 0.01) and higher distress across pregnancy (F = 22.1, p < 0.01). Mediation analyses demonstrated that the association between parity and prenatal cortisol (per area under the curve; AUC) was partially accounted for by distress (ab = 1.0, 95%CI [0.05, 2.9]). Prenatal cortisol (per AUC) did not predict postpartum depressive symptoms (b* = 0.03, p = 0.81), with no difference by parity (b* = 0.03, p = 0.91). At postpartum, a significant interaction between parity and cortisol (b* = 0.40, p = 0.03) revealed no significant association between cortisol and mood among multiparas (b* = -0.11, p = 0.28) but a trend toward a positive association among primiparas (b* = 0.24, p = 0.06).

Discussion: Cortisol levels and pregnancy-specific distress are higher in primiparas versus multiparas, with pregnancy-specific distress partially mediating the association between parity and cortisol levels. Cortisol levels and mood display correspondence at postpartum in primiparous but not multiparous women. While observational studies must be interpreted with caution due to potential unmeasured confounders, these findings suggest that future studies examining mechanisms underlying perinatal and postpartum hypothalamic-pituitary-adrenal perturbations and designing interventions aimed at preventing related complications should carefully consider potential differences by parity.