You'd best check....but I was told that omega3 from fish oil is fine but dont try and get it from flaxseed oil....something to do with too much vit B. So I found this...
Omega-3 and Pregnancy
Pregnant women are often told to take fish oil capsules but must be careful to get the best quality, instead of cheap, generic stuff. The cheap fish oil may come from fish with contamination and may not be free of pollutants. Women should be careful about the types of fish and fish oil they consume when they are pregnant, nursing, or even when experiencing pregnancy symptoms.
Flaxseed oil does have omega-3 in it and is preferred by some people however some doctors say flaxseed oil should not be taken by pregnant women.
The reason is that flax seed, like soy or even more so, seems to have an effect on estrogen and hormones and might interfere with your body during pregnancy. Ask your doctor.
One study on this was: Brooks JD, Ward WE, Lewis JE, et al. Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy. Am J Clin Nutr 2004;Feb, 79(2):318-325.
Also, flaxseed oil does not have as high an amount of DHA as fish oil, so fish oil is just better anyway at giving you the DHA you want.
Meanwhile, fish oil has been found in some studies to greatly support pregnancy and healthy baby development, and may even help prevent miscarriage. This is very, very important.
One such study was: Rossi E, Costa M., Fish oil derivatives as a prophylaxis of recurrent miscarriage associated with antiphospholipid antibodies (APL): a pilot study. Lupus 1993;2:319-23.
Conclusion: Pregnant women should talk to their doctors about avoiding flaxseed oil and also taking the most pure fish oil pills on the market.