Childbirth And Depression: Is Postpartum Depression An Illusory Correlation?

The period immediately following the birth of a child is a critical time for a number of important early developmental events and the lack of energy and ability of a mother to cope effectively with the demands of this period can constitute a serious threat to the infant’s well-being. While major depressive episodes result in the well-known attendant morbidity, including marked functional impairment, distress and increased risk of suicide, early maternal depression also puts a second individual, the child, at significant risk during what many believe to be the most critical of developmental periods.

Early maternal depression is also associated with diminished enrichment behaviors, shortened durations of breastfeeding, as well as the renewal of maternal smoking. Interactions between depressed mothers and their children are known to be of lower quality than those of non-depressed mothers which have been shown to adversely affect physical growth and neurobehavioral development.  Other research links maternal depression to the increased risk of conduct disorders and psychiatric disturbances among children, as well as greater child insecurity and anxiety- diagnoses that have been shown to persist into adulthood.

Historically, physicians have noted depressive symptoms following childbirth since the time of Hippocrates, sometime around 300BC. More recently, Hollywood celebrities including Brook Shields, Gwyneth Paltrow, Alanis Morissette, Chrissy Teigen, and Adele, have each offered their voice towards reducing the stigma associated with postpartum depression.

The recent attention in both the professional and lay literature has resulted in the folk assumption that childbirth may independently, and regularly, cause depression. However, from a scientific standpoint, an important question that remains to be answered is whether the postpartum period actually represents a time of greater vulnerability for depressive episodes.

To address this question, an international group of researchers conducted the largest and most rigorous study of postpartum depression to date. Some of these findings were recently published in the peer-reviewed journal, Archives of Women’s Mental Health.

Utilizing the entire national population of first births in Sweden between the years 1997 and 2008 and accounting for more than 700,000 individual women, findings suggest that the postpartum period is not a time of increased vulnerability for depression for most women. To conduct the study, researchers first needed to determine the overall risk of developing depression in the first year following child delivery based on each woman’s personal medical record. The result of this analysis provided a woman’s overall risk of developing postpartum depression. The next step was to assign each woman in the study with a computer-generated randomized date of child delivery. This is referred to as a phantom delivery date because it is not in any way related to the actual birth of a child.  Most importantly, this phantom delivery date had to be selected from a time period in which each woman would normally be expected to deliver a child. Once the phantom delivery date was assigned, researchers determined the woman’s risk of developing depression, again based on an actual depression diagnosis, for the full calendar year following that random date.  Surprisingly, the risk for postpartum depression was markedly lower than the risk of developing depression at some other point during her reproductive lifetime.

So why do these recent findings differ from what is commonly reported to be the most common complication of child delivery?

1) The vast number of past studies have explored postpartum depression symptomatology, whereas this study relied on clinically relevant postpartum depression diagnoses.

The difference between feeling depressed and requiring treatment is not an insignificant issue. For example, according to the diagnostic manual used by clinicians (DSM-5) who diagnose depression, a woman must have 5 of 9 symptoms consistently for two weeks to receive the diagnostic specifier associated with postpartum depression. Importantly, many of these same symptoms overlap with the common non-pathologic discomforts associated with childbirth – tearfulness, sleep difficulty, irritability, appetite and weight change, fatigue, worry, feelings of shame or guilt, indecisiveness, and difficulty concentrating. These intermittent symptoms normal to the early maternal experience are precisely why the accurate diagnosis of postpartum depression necessitates a two-stage process – the assessment of depression symptoms followed by a structured diagnostic interview. Unfortunately, for logistical reasons, both administrative and financial, the vast majority of research exploring postpartum depression has relied solely on self-reported symptom inventories such as the Edinburgh Postnatal Depression Scale (EPDS), which as a single stage process sans the prerequisite clinical assessment, can result in a gross overestimation of prevalence.  This is something even the authors of the EPDS have pointed out.

2) Most studies of postpartum depression have been conducted on small convenience samples that come from local clinics or regional hospitals and as such cannot represent every woman within a population.

The current study, which represents the largest most rigorous study of clinically relevant postpartum depression to date used a nationally inclusive dataset that included every woman who delivered their first child in the county of Sweden between January 1, 1997, and December 31, 2008. Only a handful of similar methodologically rigorous, population-based studies of postpartum depression using a two-stage diagnostic process like the current study exist. These studies, which used medical diagnoses to determine the rates of clinically significant postpartum depression in the United States, Sweden, Denmark, Finland and Great Brittan, repeatedly point to considerably lower prevalence rates than what is commonly reported. Unfortunately, because stories of lower risk do not capture attention, these studies generally go unnoticed by the public and are frequently orphaned within the professional literature.

3) The idea of depression covarying with childbirth may actually represent an illusory correlation.

There is a difference between correlation and causation and the well-established observation of depression following childbirth does not necessarily equate to causation. Indeed the history of medicine is littered with erroneous relationships such as vaccinations causing autism and full moons causing lunacy. Our tendency to perceive two events as causally related, when their relationship is coincidental (or even non-existent) is a form of cognitive bias known as illusory correlation.  The overutilization of screenings with high sensitivity and poor specificity has the potential to produce illusory correlations– a situation when clinicians may believe events or risk factors, such as depression and childbirth, are related even when they are not. Underscoring this possibly is the fact that pregnant and postpartum women represent a medically captured population, and are therefore regularly available to be screened for depressive symptomatology. It is, therefore, possible that the contemporary characterization of postpartum depression, as a common complication associated with childbirth, confuses the understanding of trigger and cause – simply because that is when they are available for screening.

Supporting this possibility is the finding that the risk postpartum depression is almost entirely explained by a woman’s history of depression. In a previous study published in the peer-reviewed journal Depression and Anxiety, using the same sample of women in Sweden, the overall risk for postpartum depression was 62 in 10,000.  However, if a woman had a prior history of depression her risk for postpartum depression rose dramatically to 1,154 in 10,000 – a 21-fold increase in risk.

Notably, the rate of postpartum depression is often stated to be about 1 in 8, but sometimes as high as 1 in 4.  While these rates have garnered considerable attention in both the professional and lay literature, empirical evidence suggest that these rates are misrepresented, clinically unreliable and potentially dangerous to continue promoting. Without question, they have led some to believe that the postpartum period is a time of unique vulnerability for mood disturbance.

Because postpartum depression impacts both the mother and her child, it is a public health concern. As such, the increased awareness of early maternal depression and the subsequent destigmatization of a very real psychological illness is welcomed progress. Notably, the increased attention has also led to initiatives directed at enhancing postpartum depression detection through universal screening programs.  However, despite considerable evidence suggesting that some women are susceptible to intense mood changes associated with the unprecedented hormonal fluctuations that occur during and immediately after pregnancy, pathologizing what for most women may represent the normal discomforts of a healthy adjustment period can be equally deleterious. By continuing to misrepresent a woman’s actual risk, saddling ill-equipped clinicians with responsibilities outside their expertise, and implying symptom screening tools alone adequately diagnose clinical depression, increases the likelihood of misdiagnoses, over-treatment and the unwarranted medicalization of an already vulnerable population.