Is Postpartum Depression a Unique Psychiatric Disorder?

For a long time, postpartum depression (PPD) lingered in the shadows, but in recent years significant efforts have been made to promote the screening and treatment of women with the disorder.

Efforts to understand PPD have led to an uptick in scientific research as well. Since 2008, the number of PPD-related scientific articles published each year has doubled, according to the scientific database PubMed.

The results of these studies have led some experts to question whether PPD is a subtype of major depressive disorder (MDD), as it is categorized in DSM-5, or a discrete psychiatric condition.

Jennifer Robertson

“I have seen many women in clinical practice who have only ever shown depressive symptoms right after giving birth,” said Samantha Meltzer-Brody, M.D., M.P.H., director of the Perinatal Psychiatry Program at the University of North Carolina. The presentation of depressive symptoms only after pregnancy is unlike MDD, which is a chronic condition, typically characterized by multiple depressive episodes.

A study recently published by Molly Fox, Ph.D., an assistant professor of psychiatry and biobehavioral sciences at the University of California, Los Angeles, and psychology professor Laura Glynn, Ph.D., of Chapman University in Los Angeles also suggests key differences between women who present with PPD and MDD.

Fox, Glynn, and their colleagues enrolled 239 women during early pregnancy and assessed them periodically over two years. They found that two clusters of symptoms showed significant differences in prevalence depending on depression onset. One cluster of symptoms related to worrying was much more frequent in women who became depressed within the first three months after delivery than women developed depression beyond the postpartum period. In contrast, symptoms related to loss of interest (anhedonia), sadness, and fatigue were much less common in women who developed depression shortly after childbirth.

“Sadness and anhedonia are two of the defining features used in making a diagnosis of major depression,” said Fox. That means that not only might PPD be different than typical depression, but perhaps that even using the word “depression” might be a misnomer, she said.

Fox acknowledged that the study was limited since all of the participants were mothers. Understanding how depressive symptoms manifest at different stages in a woman’s life will require data on women who have never given birth as well as women who become depressed while pregnant.

Additionally, she cautioned that while symptoms are easy to identify and compare, they also are naturally heterogenous; even the same individual can have two episodes of severe depression characterized by different symptoms.

Genes May Contribute to PPD

Even as some scientists try to understand PPD symptoms, others, including Meltzer-Brody, have been digging through the human genome to see if there are certain genes that might predispose women to PPD. If there are such genes and they are different from those associated with the risk of MDD, this might also support the concept of PPD as its own disorder.

Some of the first evidence of a potential difference between the genetic makeup of women who develop PPD and those who develop MDD came in a 2016 study Meltzer-Brody did along with researchers in Sweden. Making use of Swedish health registries, Meltzer-Brody and colleagues mapped the depression rates among female siblings (both twins and non-twins). They found that in cases of PPD, heredity accounted for about 50 percent of the risk, compared with about 32 percent in MDD.

Meltzer-Brody is now trying to identify which genes are involved in this familial risk of PPD. To aid in this effort, she has launched a new international consortium known as Postpartum Depression: Action Towards Causes and Treatment, or PACT. By bringing together different research groups, the currently available genetic data can be pooled together to enable more sophisticated analyses. PACT has also launched a new research project that uses smartphone apps to screen women and request DNA samples from cases of suspected PPD to add even more data to the mix (Psychiatric News, January 19).

Brain Changes During Pregnancy

It is well understood that the body undergoes significant physical and hormonal changes during pregnancy to prepare the mother for fetal growth, delivery, and nursing. Less well known is the fact that the brain also undergoes substantial changes to prepare the pregnant female for the emotional demands of motherhood, explained Kristina Deligiannidis, M.D., an associate professor at the Feinstein Institute for Medical Research.

“Believe it or not, we still haven’t characterized the normal brain changes that occur during pregnancy and the early postpartum phase,” she told Psychiatric News.

Deligianiddis and others believe that in some women one or more of these neurological changes may unmask some biological vulnerability that can trigger depression.

“In some women the trigger is revealed by changes that signal the onset of pregnancy, while in others it is likely the withdrawal process after delivery that leaves them vulnerable,” she said.

A better understanding of normal changes in the female brain over the course of pregnancy is needed so that changes associated with PPD can be identified.

Fox said she believes insights into the normal brain changes that occur in pregnancy might also provide insight into the diverging symptom profiles she has observed in postpartum women. As Fox and Glynn’s longitudinal study found, symptoms of guilt and anxiety are elevated in postpartum women with depression. However, many new mothers without PPD also have similar anxious feelings. Extra worrying about a child may not itself be pathological in the context of motherhood, Fox said, and brain scans of women who report excess worry might confirm that.

“We want to acknowledge and treat the disorder in people where symptoms are really unpleasant, but we have to be careful not to slap a label on mothers who are undergoing a normative change,” she said. ■