Is flaxseed safe during pregnancy?

What does the evidence say about flaxseed during pregnancy?

1. Some studies of flaxseed use during pregnancy suggest it is possibly unsafe, though NCCIH describes the evidence as not conclusive. 1
2. Little is known about whether flaxseed is safe to use while breastfeeding. 1
3. Flaxseed is marketed as a supplement containing alpha-linolenic acid, an omega-3 fatty acid, which is not the same molecule as the DHA prenatal products supply. 1
4. In rats, both in utero and postnatal 5 percent and 10 percent flaxseed exposure shortened mammary tumor latency, and 10 percent exposure raised tumor multiplicity in female offspring. 2
5. That same rat study pointed to cadmium accumulated in flaxseed as a possible mechanism, and rodent findings do not translate directly to people. 2

Is flaxseed safe in each trimester?

• First trimester. Flax often enters the picture as a fiber fix or a plant omega-3 source, sometimes both. This is the trimester to name it out loud at your first visit, especially if you are taking a daily flaxseed oil capsule rather than sprinkling ground seed on food.
• Second trimester. If constipation is what brought you to flax, there are better studied options for pregnancy, and your clinician can point you at one. Water, fiber from whole foods, and specific supplements have a clearer track record here.
• Third trimester. For omega-3s, algae-based DHA is the route with pregnancy-specific evidence behind it, and flax contributes alpha-linolenic acid rather than DHA directly. Worth a conversation about which one you actually want.