"I went back the second time to recover from Martin's birth, since I'd gotten dangerously anemic."

Anemia occurs when someone experiences a significant decrease in their red blood cell count. Anemia leads to a lack of oxygen in the organs, and is the most common disorder of the blood.  Symptoms include yellow skin and eyes, general fatigue and shortness of breath; in severe cases, heart failure can occur.

Anemia is most commonly caused by an iron deficiency, so a diet of iron-rich foods (or an iron supplement) is a common treatment.  However, in parts of the world where diet or resources are limited, this is not necessarily possible.