If we look at Omega-3 from the point of being a vegan or vegetarian, it's all about understanding the forms of Omega-3. We need DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid). DHA is the most important for pregnancy and for baby, but DHA and EPA as a combination is perfect.
Many vegans and vegetarians take flaxseed, chia or other seed oils, thinking that this gives them all the Omega-3 that they need, but whilst they’re great, natural products in themselves, they don’t give you the right type of Omega-3. They contain their Omega-3 in the form of ALA which is alpha-linolenic acid. ALA needs to be converted by the body into DHA or EPA before it can be absorbed and the benefits utilised. But here's the thing, that conversion is very low at best.
There is some evidence to suggest it's hit and miss, depending on your health at the time as well as your diet. For example, let’s look at someone taking 1,000mg of flax a day. Of a 1,000 mg of a good quality flax, about 500mg of that is ALA, so there's the Omega-3, but you're only going to get about a tenth of that converted into EPA or DHA. That means from a thousand milligrams, the best case scenario is that they’re getting just a maximum of 50 milligrams of useful, bioavailable Omega-3.
To put that into context, it means that someone would have to take about 20 days worth of flaxseed to get the same as one day’s worth of a good quality vegan/vegetarian approved EPA & DHA supplement!