Which trimester is an especially critical period when poor nutrition or drug use can result in birth defects?

The first trimester is the most critical 

Adescription of  congestive heart  failure, its symptoms, risk factors, and treatment. to the  heart muscle  other than by artery or blood  flow  problems; signs of  heart  failure may not  meanthe patient has  heart  failure and they quit alcohol, or at least consume alcohol within the national recommended  limits.