Effect measured in women already diagnosed with mood disorders.
In a small–scale study of women with previously diagnosed mood disorders, Johns Hopkins researchers report that lower levels of the hormone allopregnanolone in the second trimester of pregnancy were associated with an increased chance of developing postpartum depression in women already known to be at risk for the disorder.

In a report on the study, published online on March 7 in the journal Psychoneuroendocrinology, the researchers say the findings could lead to diagnostic markers and preventive strategies for the condition, which strikes an estimated 15 to 20 percent of American women who give birth.

The researchers caution that theirs was an observational study in women already diagnosed with a mood disorder and/or taking antidepressants or mood stabilizers, and does not establish cause and effect between the progesterone metabolite and postpartum depression. But it does, they say, add to evidence that hormonal disruptions during pregnancy point to opportunities for intervention.

For the study, 60 pregnant women between the ages of 18 and 45 were recruited by investigators at study sites at The Johns Hopkins University and the University of North Carolina at Chapel Hill. About 70 percent were white and 21.5 percent were African–American. All women had been previously diagnosed with a mood disorder, such as major depression or bipolar disorder. Almost a third had been previously hospitalized due to complications from their mood disorder, and 73 percent had more than one mental illness.

During the study, 76 percent of the participants used psychiatric medications, including antidepressants or mood stabilizers, and about 75 percent of the participants were depressed at some point during the investigation, either during the pregnancy or shortly thereafter.

During the second trimester (about 20 weeks pregnant) and the third trimester (about 34 weeks pregnant), each participant took a mood test and gave 40 milliliters of blood. Forty participants participated in the second–trimester data collection, and 19 of these women, or 47.5 percent, developed postpartum depression at one or three months postpartum. The participants were assessed and diagnosed by a clinician using criteria from the Diagnostic and Statistical Manual of Mental Disorders, version IV for a major depressive episode.

Of the 58 women who participated in the third–trimester data collection, 25 of those women, or 43.1 percent, developed postpartum depression. Thirty–eight women participated in both trimester data collections.

Using the blood samples, the researchers measured the blood levels of progesterone and allopregnanolone, a byproduct made from the breakdown of progesterone and known for its calming, anti–anxiety effects.

The researchers found no relationship between progesterone levels in the second or third trimesters and the likelihood of developing postpartum depression. They also found no link between the third–trimester levels of allopregnanolone and postpartum depression. However, they did notice a link between postpartum depression and diminished levels of allopregnanolone levels in the second trimester.

For example, according to the study data, a woman with an allopregnanolone level of 7.5 nanograms per milliliter had a 1.5 percent chance of developing postpartum depression. At half that level of hormone (about 3.75 nanograms per milliliter), a mother had a 33 percent likelihood of developing the disorder. For every additional nanogram per milliliter increase in allopregnanolone, the risk of developing postpartum depression dropped by 63 percent.