Inclusion Criteria:
* Age 18-55
* All individuals must be 14-34 weeks gestational age or within one year of delivery at the time of treatment. The odds of delivery nears 10% after 36 weeks, which would limit participants from being able to complete the study and interfere with the primary study aim to understand safety and tolerability. Additionally, after 36 weeks, the standard of care is weekly obstetric check-in visits, which would be challenging for patients to complete given the time demands of the study protocol.
* Patients will not be scanned after 32 weeks gestational age due to the time needed to construct the individualized treatment target. Individuals seeking treatment beyond 32 weeks will be offered scalp-based target localization so as not to limit patient access to care.
* English proficiency sufficient for informed consent, questionnaires/tasks, and treatment
* Primary diagnosis of major depressive disorder per DSM-V criteria (MINI International Neuropsychiatric Interview/ Structured Clinical Interview for DSM-5): \>20 on the Montgomery-Åsberg Depression Rating Scale (MADRS) and moderate to severe level of treatment resistance (Maudsley Staging Method)
* Stable antidepressant medication regimen, or remain medication free, for 4 weeks prior to treatment and to remain on this regimen throughout the treatment course. We request that this regimen remain stable until the 1 month post-treatment if clinically appropriate.
* Primary clinician (e.g. psychiatrist, therapist, psychologist, APRN, PA, etc.) responsible for psychiatric care before, during, and after the trial in addition to an obstetric provider responsible for obstetric care.
* Agreement to lifestyle considerations: Continue usual intake patterns of caffeine- or xanthine-containing products (e.g. coffee, tea, soft drinks, chocolate) throughout treatment
Exclusion Criteria:
* Concurrent use of rapid acting antidepressant agent (ketamine/esketamine/ECT)
* Receiving or planning to receive other TMS treatments during course of participation
* Obstetric concerns: Preeclampsia and/or current frequent, painful contractions (more than one every 10 minutes)
* History of: Neurosurgical intervention for depression, autism spectrum disorder, intellectual disability, severe cognitive impairment, significant neurological illness (e.g., dementia, Parkinson's, Huntington's, brain tumor, seizure disorder, subdural hematoma, multiple sclerosis, brain lesion), untreated or insufficiently treated endocrine disorder, and/or treatment with investigational drug or intervention during the study period
* ≥ 30% change in MADRS score between screening and baseline
* Anyone presenting with: Mania or hypomania, psychosis, active suicidal ideation with plan and some intent to act or a suicide attempt (defined by C-SSRS) within the past 3 months, neurological lesion, contraindications to either TMS or MRI (e.g., metallic implants, severe insomnia \> 4 hours per night with hypnotic, etc.), and/or current moderate or severe substance use disorder or demonstrating signs of acute substance withdrawal
* Existing tinnitus (ringing in the ears) that causes functional impairment
* History of retinal detachment or other retinal pathology
* Severe borderline personality disorder
* Any other condition deemed by the PI to interfere with the study or increase risk to the participant
