Is it safe to take resveratrol while pregnant or breastfeeding?

Unknown. Resvertrol from organic grape seed pomace would be safe after the first trimester. It might be helpful for someone with metabolic syndrome. The usual forms from japanese knotweed might not be safe. Certainly there would be no real advantages for mother or baby.
Yes. Resveratrol is an "anti-aging" antioxidant found in red wine. As a health and wellness physician, I am a big supporter of many supplements which may have additional health benefits. Resveratrol has no negative effects, and may be taken during pregnancy and lactation, if desired.