For sure an eating disorder will have negative effects on a pregnancy. In the first trimester the fetus needs the essential nutrients to begin to develop properly. Later on in the pregnancy the fetus needs to gain weight. Mom's with eating disorders often have preterm babies, or babies with low birth weight.
Developmental problems such as cerebral palsy and low IQ can occur in the child. There is also a higher risk of cardiac problems, liver problems, cleft palate etc.
Ultimately the baby can die from mom having an eating disorder.
Usually severe anorexics or bulimics will not be able to get pregnant because they don't get normal periods, or ovulate all the time. This is the body's way of protecting the unhealthy mother from pregnancy, and the potential fetus.
Check out eating disorders and pregnancy on google, there's tons of info.