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

Maternal depression can have a significant harmful influence on both mothers and children. Considering the possibility of adverse effects of antidepressants and previous meta-analyses showing the positive effects of omega-3 polyunsaturated fatty acids (PUFAs) supplementation in reducing depressive symptoms, omega-3 PUFAs may provide a safe strategy. The investigators evaluate efficacy and safety of omega-3 PUFAs for pregnant women with depressive symptoms. (Participants who skipped taking supplements for more than 7 days will be excluded from a per protocol analysis.)

Inclusion Criteria:

1. pregnant women aged 20 years or older
2. between 12-24 weeks gestation
3. a Japanese conversational ability in Japan site or a Mandarin conversational ability in Taiwan site to understand the scope of the present trial and to provide written consent for study participation
4. planned to take assessments 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. Serious psychiatric symptoms such as self-harm behavior or in need of rapid psychiatric treatment
3. difficult to expect a normal birth (ex: fetal malformation etc.)
4. having a history of bleeding disorder such as von Willebrand's Disease
5. regular treatment with aspirin or warfarin within the last 3 months
6. a smoking habit of ≥40 cigarettes per day
7. regular treatment with ethyl icosapentate or regular consumption of omega-3 PUFA supplements within the last 3 months
8. a habit of eating fish as a main dish ≥4 times per week.