Objective
To investigate the possible association between postpartum depressive symptoms and season of delivery.
Study Design
During 1 year, delivering women in the Uppsala University Hospital were asked to participate in the study by filling out 3 postpartum questionnaires containing the Edinburgh Postnatal Depression scale and questions assessing life style, medical history, breastfeeding, and social support.
Results
Two thousand three hundred eighteen women participated. Women delivering in the last 3 months of the year had a significantly higher risk of self-reported depressive symptomatology both at 6 weeks (odds ratio, 2.02, 95% confidence interval, 1.32–3.10) and at 6 months after delivery (odds ratio, 1.82, 95% confidence interval, 1.15–2.88), in comparison to those delivering April-June, both before and after adjustment for possible confounders.
Conclusion
Women delivering during the last quartile of the year had a significantly higher risk for depressive symptoms 6 weeks and 6 months postpartum and would thus benefit from a closer support and follow-up after delivery.
Postpartum depression (PPD) is considered as one of the most common complications of childbirth and a major cause of maternal mortality worldwide. The risk of developing PPD within the first year after childbirth is estimated to approximately 10-20% in western societies, according to recent studies. PPD is characterized by depressive symptoms beginning within the first 4 weeks after childbirth, or defined as the development of a mood disturbance 2 weeks to 1 year after delivery, with symptom onset most often during the first 3 months postpartum. The development of depressive symptoms in the new mother or father can have devastating consequences for both parents and infant, because PPD has been associated with attachment difficulties, as well as an increased risk for sudden infant death syndrome and cognitive disturbances in the child during critical stages of development in infancy and childhood.
The seasonal variation of symptoms in a variety of mental disorders is well documented. The seasonality patterns of bipolar disorder, suicide, and the Seasonal Affective Disorder (SAD) have been studied extensively. SAD affects approximately 1-6% of the general population, and is characterized by major depressive episodes that cycle in response to season, with symptoms generally worsening in the winter, although some patients experience a worsening of mood in the summer. SAD is more prevalent in women than in men, especially during the childbearing years, and there have also been suggested associations between seasonal mood changes and various climatic variables, most profoundly daylight, which may mediate alterations in the cortical and subcortical serotonergic systems.
The seasonal variations in PPD, in contrast, have not been thoroughly explored. A Finnish study by Hiltunen et al, including 185 women evaluated postpartum, suggested an increased prevalence of mild depression in the autumn immediately after delivery. Even when seasonality was classified according to the amount of light, depression was more prevalent during the dark months, namely, October, November, December, and January. Corral et al found a higher prevalence of SAD in the PPD group when compared with controls, but no predictive value of the Seasonal Pattern Assessment Questionnaire when trying to foresee PPD. In an American study using data from the Pregnancy Risk Assessment Monitoring System (PRAMS), no association between depressive symptoms postpartum and season of birth or length of daylight at birth was noted. A recent pilot study by Panthangi et al in Detroit, MI, displayed a slight seasonal variation in PPD, with women giving birth during the autumn and winter having a higher risk for PPD. However, the results were not statistically significant, because the study was underpowered.
In Scandinavia, the seasons vary greatly with a profound effect on the daylight period. Thus, Scandinavia is an advantageous geographical area to assess seasonal patterns. The aim of this study was to determine the effect of season of delivery on the risk for PPD in a population based sample of Swedish women. We hypothesized that delivery during the darkest months of the year would be associated with increased risk of developing PPD.
Materials and Methods
This study was undertaken as part of the UPPSAT project, a population-based cohort study in the county of Uppsala, Sweden, investigating correlates of postnatal depression in Sweden. The study was conducted at the Department of Obstetrics and Gynecology at Uppsala University Hospital. Uppsala is a medium-sized Swedish county with a population of 323,270 inhabitants and the University Hospital is responsible for all delivering women within the county, as well as high-risk pregnancies from nearby counties.
Study population
From May 21, 2006, to June 26, 2007, all eligible women giving birth at Uppsala University Hospital were contacted by their midwife or midwife’s assistant after delivery and asked about their willingness to take part in a longitudinal study of maternal, paternal, and infant well-being. Exclusion criteria were (1) not being able to adequately communicate in Swedish, (2) women with confidentially kept personal data and (3) women with intrauterine demise or with infants immediately admitted in the neonatal intensive care unit.
The mothers received both oral and written information about the study objectives and written consent was obtained. The study subjects completed a self-administered structured questionnaire containing the Edinburgh Postnatal Depression Scale (EPDS) 5 days after delivery. Two more questionnaires were sent to the study subjects, one at 6 weeks after delivery and one at 6 months after delivery. The women were instructed to complete and send back the questionnaires to the hospital by post.
Study variables and outcome measures
The structured questionnaires included questions on physical and sociodemographic characteristics, medical, psychiatric, gynecologic and obstetric history variables, lifestyle, diet and medication parameters, variables assessing social network and support, questions on breastfeeding, and the Swedish version of the EPDS. Variables concerning the delivery and neonatal outcome were retrieved from the medical records.
The EPDS has been validated in Sweden and has a cutoff at 11.5 points after which a mother is screened positive for PPD. It is usually not used as a screening instrument during the first 2 weeks after delivery, because of the high percentage of postpartum blues occurring during this time. For the current study, the EPDS-based (self-reported) PPD status at 6 weeks and 6 months postpartum were used as the main outcome measures.
Statistical analyses
The data were first cross-tabulated according to self-reported PPD status at 5 days, 6 weeks, and 6 months postpartum and month of delivery. The procedure was then repeated separately for women with and without previous psychiatric contact (visit to a psychiatrist or a psychologist before delivery).
The data were subsequently modeled through multiple logistic regression, using self-reported PPD at 5 days, 6 weeks, and 6 months after delivery as the outcome variable and year quartiles as predictor variables. The first quartile included January, February, and March, the second one April, May, and June, the third one July, August, and September, and the fourth one October, November, and December. Previous psychiatric history, breastfeeding, reported partner support, maternal education, stressful life events, and whether the current pregnancy was planned or not were treated as potential confounders and were later also included in the logistic regression analysis. To not compromise the power of the study by including 5 different variables in the logistic regression model apart from previous psychiatric contact, a score of “maternity stressors” was constructed from among the possible confounders. Mothers received 1 point for each 1 of the following: not breastfeeding, not considering their partner as supportive, having low educational status, having experienced at least 1 stressful life event in the past months, and having had an unplanned pregnancy. The sum of these points consisted the “maternity stressors score.” The second quartile of the year was considered as the baseline, because June was the month with the lowest mean reported EPDS score over a 6-month period, and also because June is the brightest month in Sweden.
SPSS version 17.0 (SPSS, Inc, Chicago, IL) was used for the statistical analyses. Statistical significance was set at a P value of < .05.
The study protocol was approved by the Regional Research and Ethics Committee of Uppsala.
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