Introduction
The interest in the function of the hypothalamic-pituitary-adrenal
(HPA)-axis of pregnant women is growing, as evidenced by the evolving
literature revealing the influence of maternal stress on the offspring´s
physical and mental health outcomes 1-5.
However, the evidence regarding whether prenatal maternal cortisol
levels are the sole or main mediating link is
conflicting6. It also seems that foetal vulnerability
to high maternal cortisol levels varies across the gestational
phases4, 6-8.
Research regarding the impact of cortisol in the mediation of maternal
stress upon the foetus is complicated by the fact that the HPA-axis
activity shows substantial diurnal variability 9 in
addition to individual differences. Single cortisol measures in plasma
or saliva may therefore not sufficiently reflect the overall long-term
biological activity of cortisol. Analysis of hair cortisol
concentrations (HCC) is used to overcome such
limitations10-12, where one cm of hair corresponds to
about one month´s cortisol accumulation13. This method
has been validated against cortisol in saliva across the pregnancy and
postpartum periods and has proved to be a reliable metric of HPA
activity, enabling estimation of integrated cortisol
release14.
Reports on HCC throughout pregnancy have revealed varying results,
probably due to the different analysis methods used11,
14-18. The research focus has also been wide-ranging and has shown
several factors of importance for HCC, including season,
obesity11,19 and delivery mode 11.
In addition, some 18-19 researchers have noted a
relation between psychosocial and lifetime stress exposure on HCC during
pregnancy, while others 20 have concluded that neither
psychological distress, nor chronic stress or psychiatric symptoms had
any impact.
Higher cortisol levels have been reported in primiparae versus
multiparae21-22, probably related to more pregnancy
distress 23. However, Federenko et al. in 2006 could
not detect any effect of parity on cortisol levels22.
HCC covering single-month periods may give more precise and more
coherent results when investigating relations to childbirth and neonatal
outcomes, but to our knowledge, no reports of measurements conducted on
a monthly basis are available regarding HCC during pregnancy and
postpartum. We hypothesised that there may be variations in cortisol
hair levels during pregnancy and postpartum, possibly influenced by
parity. Hence, the purpose of this study is to add to the knowledge of
normal HPA-axis functioning during pregnancy and postpartum by
determining HCC levels on a monthly basis. A second aim was to explore
further differences in HCC levels associated with parity during
pregnancy.