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In comparison with the vast epidemiological literature on postpartum depression (PPD), relatively few studies have examined the biological aspects of the disorder. However, research into the biological mechanisms of PPD is a challenging task, as normal pregnancy and the postpartum period cause adaptive endocrine changes, which would otherwise be considered pathological in nonpregnant women. This review focuses on the adaptive changes of childbearing and nursing, which ultimately may put women at increased risk of PPD. In light of the normal physiology, the authors also attempt to describe the current evidence of the biological changes associated with the development of depression in the postpartum period, including ovarian steroids, the hypothalamic-pituitary-adrenal axis, the serotonergic neurotransmitter system, the thyroid system and inflammatory markers. In addition, current knowledge on candidate genes associated with PPD is reviewed.

ObjectivesTo explore the association between postpartum haemorrhage (PPH) and postpartum depression (PPD), taking into account the role of postpartum anaemia, delivery experience and psychiatric history.MethodsA nested cohort study (n = 446), based on two population-based cohorts in Uppsala, Sweden. Exposed individuals were defined as having a bleeding of ≥1000ml (n = 196) at delivery, and non-exposed individuals as having bleeding of <650ml (n = 250). Logistic regression models with PPD symptoms (Edinburgh Postnatal Depression scale (EPDS) score ≥ 12) as the outcome variable and PPH, anaemia, experience of delivery, mood during pregnancy and other confounders as exposure variables were undertaken. Path analysis using Structural Equation Modeling was also conducted.ResultsThere was no association between PPH and PPD symptoms. A positive association was shown between anaemia at discharge from the maternity ward and the development of PPD symptoms, even after controlling for plausible confounders (OR = 2.29, 95%CI = 1.15–4.58). Path analysis revealed significant roles for anaemia at discharge, negative self-reported delivery experience, depressed mood during pregnancy and postpartum stressors in increasing the risk for PPD.ConclusionThis study proposes important roles for postpartum anaemia, negative experience of delivery and mood during pregnancy in explaining the development of depressive symptoms after PPH.

Recent studies indicate that the immune system adaptation during pregnancy could play a significant role in the pathophysiology of perinatal depression. The aim of this study was to investigate if inflammation markers in a late pregnancy plasma sample can predict the presence of depressive symptoms at eight weeks postpartum. Blood samples from 291 pregnant women (median and IQR for days to delivery, 13 and 7-23days respectively) comprising 63 individuals with postpartum depressive symptoms, as assessed by the Edinburgh postnatal depression scale (EPDS≥12) and/or the Mini International Neuropsychiatric Interview (M.I.N.I.) and 228 controls were analyzed with an inflammation protein panel using multiplex proximity extension assay technology, comprising of 92 inflammation-associated markers. A summary inflammation variable was also calculated. Logistic regression, LASSO and Elastic net analyses were implemented. Forty markers were lower in late pregnancy among women with depressive symptoms postpartum. The difference remained statistically significant for STAM-BP (or otherwise AMSH), AXIN-1, ADA, ST1A1 and IL-10, after Bonferroni correction. The summary inflammation variable was ranked as the second best variable, following personal history of depression, in predicting depressive symptoms postpartum. The protein-level findings for STAM-BP and ST1A1 were validated in relation to methylation status of loci in the respective genes in a different population, using openly available data. This explorative approach revealed differences in late pregnancy levels of inflammation markers between women presenting with depressive symptoms postpartum and controls, previously not described in the literature. Despite the fact that the results do not support the use of a single inflammation marker in late pregnancy for assessing risk of postpartum depression, the use of STAM-BP or the novel notion of a summary inflammation variable developed in this work might be used in combination with other biological markers in the future.

Background: Allopregnanolone (3α-hydroxy-5α-pregnan-20-one) is a neurosteroid which has an inhibitory function through interaction with the GABA_A receptor. This progesterone metabolite has strong sedative and anxiolytic properties, and low endogenous levels have been associated with depressed mood. This study aimed to investigate whether the very high serum allopregnanolone levels in late pregnancy covary with concurrent self-rated symptoms of depression and anxiety. Methods: Ninety-six women in pregnancy weeks 37-40 rated symptoms of depression and anxiety with the Montgomery-Åsberg Depression Rating Scale (MADRS-S) and Spielberger State-Trait Anxiety Inventory. Their serum allopregnanolone was analyzed by Celite chromatography and radioimmunoassay. Results: Ten women had elevated depression scores (MADRS-S ≥13), and this group had significantly lower allopregnanolone levels compared to women with MADRS-S scores in the normal range (39.0 ± 17.9 vs. 54.6 ± 18.7 nmol/l, p = 0.014). A significant negative correlation was found between self-rated depression scores and allopregnanolone concentrations (Pearson's correlation coefficient = -0.220, p = 0.031). The linear association between self-rated depression scores and allopregnanolone serum concentrations remained significant when adjusted for gestational length, progesterone levels, and parity. Self-rated anxiety, however, was not associated with allopregnanolone serum concentrations during pregnancy. Conclusion: High allopregnanolone serum concentrations may protect against depressed mood during pregnancy.