Studies have demonstrated associations between omega-3s, omega-6s, and body mass index. In this study, the levels of omega-3 in pregnancy were studied for their effect on weight retention after childbirth, which can contribute to long-term obesity.
653 pregnant women were tested at 26-28 wk of gestation for levels of omega-3 and omega-6.  The median retained weight of women was 0.90 kilograms at 18 mo after pregnancy. Of 653 women, 544 women had gained <5 kilograms and 109 had gained ≥5 kilograms. A statistical analysis showed that higher blood levels of EPA, DHA, and Omega-3s were associated with lower weight gain after pregnancy, whereas a higher ratio of Omega-6 to Omega-3 was associated with a more weight gain after pregnancy.
The researchers concluded:
Higher levels of Omega-3s and a lower ratio of Omega-6 to Omega-3 in the late-second trimester of pregnancy are associated with less weight retention at 18 months. This may offer an alternative strategy to assist post-pregnancy weight reduction by increasing EPA and DHA status together with a decreased ratio of Omega-6 to Omega-3 through diet or fish-oil supplementation during pregnancy.