This study is a randomized control trial (RCT) evaluating a Prenatal Walking Program (PWP) in comparison to a Postpartum Prep Program (PPP) comparison group for pregnant women experiencing depressive symptoms. In addition to assessing changes in depressive symptoms, the investigators will examine other key maternal outcomes (maternal functioning, pain, anxiety, stress, fatigue), as well as infant outcomes including birth record data (gestation, weight, Apgar scores, etc) and careful, in-person assessment of infant neurobiological functioning at 30 days postpartum.

Depressive symptoms are prevalent among pregnant women, and they are consistently linked with adverse outcomes for both women and infants, including higher rates of spontaneous abortion, preeclampsia, operative delivery, and postpartum depression. Additional risks to offspring include pre-term delivery, neonatal growth retardation, low birth weight, and delayed developmental milestones. In spite of these risks, the vast majority of affected women do not pursue any type of mental health treatment. Many women are reluctant to use antidepressants - or anything that could potentially harm the baby - prenatally. Because pregnant women have unique concerns regarding treatment acceptability, a critical need exists to develop interventions that are not only efficacious in reducing depressive symptoms, but are also viewed as acceptable by pregnant women.

Increased physical activity has numerous advantages as a strategy for improving mood during pregnancy, and prior research has shown that physical activity interventions can be effective in treating depressive symptoms in the general population. Physical activity interventions are also inexpensive, safe, and associated with a variety of positive health outcomes.

In spite of its potential as an acceptable and efficacious strategy for improving prenatal mood, few studies have evaluated physical activity as an intervention for pregnant women with depressive symptoms. Existing exercise programs that have been tested for reducing depressive symptoms in the general population are not likely to be appropriate or feasible for pregnant women. In light of this important gap, the investigators interdisciplinary team developed a gentle, 10-week, pedometer walking intervention tailored for pregnant women, the Prenatal Walking Program (PWP) and preliminarily evaluated PWP in an open trial, finding the intervention to be safe, feasible, and acceptable.

The current RCT will now evaluate PWP in comparison to a health education control comparison group tailored for perinatal women, called the Postpartum Prep Program (PPP). In addition to assessing changes in depressive symptoms, the investigators will examine other key maternal outcomes (maternal functioning, pain, anxiety, stress, fatigue), as well as infant outcomes including birth record data and in-person assessment of infant neurobiological functioning. Further, the investigators will examine evidence for potential behavioral, psychological, and biological mechanisms of action that mediate a possible treatment effect. Up to 152 pregnant women reporting elevated depressive symptoms during the current pregnancy will be enrolled and randomized into one of two groups, PWP or PPP, and will participate in blinded follow-up evaluations at multiple time-points throughout pregnancy and postpartum.

Inclusion Criteria:

1. women aged 18 or over
2. 12-27 weeks gestation with a healthy singleton pregnancy
3. English-speaking
4. cleared by prenatal provider for moderate intensity exercise
5. experiencing moderate depressive symptom elevations at time of enrollment (QIDS-C; 8-20); (6) physically inactive or low-active at time of enrollment (mean < 90 minutes/week of moderate intensity exercise, over the last 3 months).

Exclusion Criteria:

1. recently started pharmacologic or psychosocial treatment for depressive symptoms within the past 4 weeks, or recently changed dose or treatment regimen in the past 4 weeks

2. current/recent acute suicidal symptoms

3. current substance use disorder

4. psychotic symptoms or cognitive impairment

5. current eating disorder

6. current or lifetime bipolar disorder, schizophrenia, or schizoaffective disorder.

   • Finally, while the following will not exclude participants from enrollment in the study, women meeting these two criteria will be excluded from participating in the blood draw component examining inflammatory markers:

7. current significant physical or neurological illness, ie., acute or chronic infectious, inflammatory or immune disorders

8. regular use of aspirin or non-steroidal anti-inflammatory drugs.