I'd go with HIV because you will have a much easier time finding good info. With moderate/severe anorexia most women do not ovulate, which means they can't even get pregnant in the first place.
forget going with the easier one...go with the one that might affect more young pregnant moms...i would do not just anorexia, but widen it to "eating disorders while pregnant" many girls worry about getting "too big" while pregnant while others think they can eat huge amounts because they are pregnant, you can show the cause and effect on each disorder