Yes this is critical. The other part of the lamictal pregnancy study showed that if you are taking a drug with statistically significant increased risk of birth defects in pregnancy, a mega-dose of folic acid can help mitigate the risk. I believe dose is at least 3x amount in OTC prenatal vitamins. In USA there is a prescription formulation of folic acid that helps in this case (also supposed to assist with elevating mood, doesn’t do a great job of that IMHO). This formulation is not available in Canada and can only be replaced with an expensive fistful of OTC folic acid supplements daily.

If you choose to take lamictal in pregnancy a mega-dose of folic acid with it is gold standard treatment, ask your doctor.