••• Chapter 3^ Physiology of Normal Pregnancy^31
❍ What hemoglobin concentration should be considered abnormal in a pregnant woman?
Values below 11.0 g/dL are present in only 6% of normal pregnant women taking iron and are considered to be
in the range for anemia in the first and third trimesters. A patient should be considered anemic in the second
trimester if the hemoglobin value is <10.5 g/dL. Value less than these numbers should prompt a workup for
anemia.
❍ What is the most helpful parameter to make the diagnosis of iron deficiency anemia in a pregnant woman?
MCV, as it is one of the only hematologic parameters not changed during pregnancy in women not taking
iron and is increased in women taking iron. Microcythemia is only caused by three entities—thalassemia, iron
deficiency, and lead poisoning. A progressive decrease in MCV to below 82 mm^3 is usually a sign of iron deficiency
as the other causes are rare and easily ruled out.
❍ Describe the normal white blood cell count in pregnancy.
Normal range is 5,000 to 12,000/mL. During labor and the puerperium, it may increase markedly to 25,000 or
more.
❍ Which type of immunity (cell mediated vs. humoral) is affected by pregnancy and how?
Clinical evidence shows that cell-mediated immunity is weakened (Th1 responses) and humoral immunity,
immunosuppression, is strengthened (Th2 responses). Th1 and Th2 cells are functionally distinct subsets of CD4+
T-lymphocytes or helper cells. The weakened cell-mediated immunity is responsible for the decreased production
of IL2, gamma interferon, and tumor necrosis factor by the Th1 cells that are harmful to the maintenance of
pregnancy. The strengthened humoral immunity is responsible for the increase in immunosuppressive cytokines
IL4 and IL10 produced by the Th2 cells.
❍ What is the physiology of the maternal immune system in pregnancy in general terms?
Pregnancy represents a 50% allograft from the paternal contribution. As a result there is a general suppression of
immune function. Therefore, one might have increased susceptibility to infections, improvement in the humoral-
mediated autoimmune diseases, and worsening of other cellular-mediated autoimmune diseases.
❍ Does the platelet count change in normal pregnancy?
Yes. There is a moderate decrease in the number of platelets per unit volume; however, the normal range
remains the same for pregnant women (150,000–450,000/mm^3 ). The mechanism is not clear. Dilution may
contribute, but there is some evidence of increased consumption in pregnancy. Thrombocytopenia is defined as
platelets <100,000/mm^3.
❍ Is the bleeding time affected by pregnancy?
No. Bleeding times are not different when compared with nonpregnant women.
❍ By how much does the maternal resting heart rate increase in pregnancy?
10 to 15 beats per minute.
❍ Describe the change in the position and size of the heart in pregnancy.
The heart is displaced 15 degrees to the left and upward and is rotated laterally causing a larger silhouette in
radiographs. The cardiac volume may increase by 10% between early and late pregnancy.