Objective: To investigate hair cortisol concentrations (HCC) monthly in pregnant women and to explore the effect of parity. Design: Prospective cohort study from gestational week (GW) 26, at childbirth and postpartum. Setting: An antenatal care clinic in southeast Sweden. Sample: 390 pregnant women. Methods: Cortisol was measured using radioimmunoassay in methanol extracts of ground hair samples. Main outcome measures: Hair cortisol concentrations Results: Both primi- and multiparae exhibited an increase in HCC throughout pregnancy. Primiparae had significantly higher HCC in the latter part of the last trimester compared to multiparae (one month p=0.003 and two months p=0.038). The use of psychotropic medication in the first trimester correlated to HCC postpartum (p<0.001). HCC in GW 14-17 were associated with HCC in GWs 18-21 (primiparae and multiparae, p<0.001), GW 22-25 (primiparae p=0.036 and multiparae p=0.033), and two months postpartum (primiparae p=0.049). HCC in GW 18-21 was associated with GW 22-25 among both primiparae (p<0.001) and multiparae (p<0.001) as well as two months prior to childbirth among primiparae (<0.037). In general, all estimates of HCC in pregnancy and postpartum showed a significant association between HCC for a specific month and the HCC in the previous month (all p<0.001), except for the association of HCC among primiparae in GW 22-25 and three months prior to childbirth. Conclusions: Increased cortisol concentrations in hair were observed during pregnancy, which decreased three months prior to childbirth in multiparae. The results indicate a quicker suppression of the hypothalamic CRH production by placenta CRH in multiparous women.