The present study aims to examine the efficacy and safety of omega-3 polyunsaturated fatty acids for pregnant women with depressive symptoms.

Inclusion Criteria:

1. pregnant women aged 20 years or older.
2. between 12-24 weeks gestation.
3. a Japanese conversational ability to understand the scope of the present trial.
4. planned to return to the hospital for checkup at 4-6 weeks after childbirth.
5. an Edinburgh Postnatal Depression Scale (EPDS) score is 9 or more.
6. to have good physical health judged by obstetricians.

Exclusion Criteria:

1. history and current suspicion of psychosis or bipolar I disorder or substance-related disorder or eating disorder or personality disorder.
2. the item of EPDS concerning suicide ideation is 2 or more.
3. other serious psychiatric symptoms such as self-harm behavior or in need of rapid psychiatric treatment.
4. difficult to expect a normal birth (ex: fetal malformation etc.).
5. having a history of bleeding disorder such as von Willebrand's Disease.
6. regular treatment with aspirin or warfarin within the last 3 months.
7. a smoking habit of ≥40 cigarettes per day.
8. regular treatment with ethyl icosapentate or regular consumption of omega- 3 PUFA supplements within the last 3 months.
9. a habit of eating fish ≥4 times per week.