Awoman's pregnancy has been uneventful, and she has gained 25 lb (11.3 kg). at term her hemoglobin level is 10.6 g/dl (106 mmol/l) and her hematocrit is 31%. what is the physiologic reason for these hemoglobin and hematocrit levels?

Hemoglobin is a protein in red blood cells that carries oxygen throughout the body.

It indicates anemia, in women, when hemoglobin levels are lower than 12 grams per deciliter. 

It's common to happen in pregnant women.

Hematocrit is also lower that normal  ( 36 to 48% for women). Hematocrit is the fraction of blood that is made up of red blood cells. It's important to be measure when suspecting of anemia.

that is wrong, its not thymus.