Mean Corpuscular Volume (MCV)

MCV may increase slightly in normal pregnancy due to physiologic macrocytosis, but is usually within or near the nonpregnant range.

Units	Nonpregnant Adult	1st Trimester	2nd Trimester	3rd Trimester
µm³	79–93	85–97.8	85.8–99.4	82.4–100.4
fL	79–93	85–97.8	85.8–99.4	82.4–100.4

Pregnancy physiology

Mild macrocytosis is common and physiologic in pregnancy.
Often related to increased plasma volume and RBC turnover.
Typically does not exceed 100 fL unless deficiency is present.

Chanarin et al. demonstrated a consistent rise in MCV during normal pregnancy without iron or folate deficiency.

Causes of low MCV (microcytosis)

Iron deficiency anemia — most common cause in pregnancy
Anemia of chronic inflammation
Thalassemia trait (α or β)
Hemoglobinopathies (HbE disease, sickle cell variants)
Sideroblastic anemia (rare)
Lead toxicity

Cited references:
• Dunning & Fischbach, Manual of Laboratory & Diagnostic Tests, 7th ed. • Abbassi-Ghanavati M et al., Obstet Gynecol. 2009. • Gronowski AM. Laboratory Testing in Pregnancy.

Causes of high MCV (macrocytosis)

Normal pregnancy (physiologic macrocytosis)
Vitamin B12 deficiency (malabsorption, pernicious anemia, gastric surgery)
Folate deficiency (malnutrition, alcoholism, increased demand)
Hypothyroidism
Liver disease
Myelodysplastic syndromes
Medications: methotrexate, hydroxyurea, zidovudine, anticonvulsants

Cited references:
• Chanarin I et al., Br J Obstet Gynaecol. 1977. • Wallach J. Interpretation of Diagnostic Tests. • Dunning & Fischbach, Laboratory & Diagnostic Tests.

References

Lockitch G. Handbook of Diagnostic Biochemistry and Hematology in Normal Pregnancy. CRC Press, 1993.
Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
Fischbach FT, Dunning MB. A Manual of Laboratory and Diagnostic Tests, 7th ed. LWW, 2004.
Chanarin I, et al. The physiological macrocytosis of pregnancy. Br J Obstet Gynaecol. 1977;84:504–8.