When is it most important to take omega 3 while pregnant?

I am 6months pregnant and read I should take a seperate Omega 3 supplememnt(without fish oil to avoid mercury) for babys brain developement and eyes.I wasnt told by my doctor is it too late in my pregnancy to make a difference?|||It's best to take it throughout your pregnancy. However, I believe it is most critical during the first trimester because that is when the baby's organs are developing.