For prevention of megaloblastic anemia, a diet should contain suicient folic acid. The role of folate deiciency in the genesis of neural-tube defects has been well studied (Chap. 13, p. 270). Since the early 1990s, nutritional experts and the American College of Obstetricians and Gynecologists (2016a) have recommended that all women of childbearing age consume at least 400 �g of folic acid daily. More folic acid is given with multifetal pregnancy, hemolytic anemia, Crohn disease, alcoholism, and inflammatory skin disorders. Women with a family history of congenital heart disease may also benefit from higher doses (Huhta, 2015). Women who previously have had infants with neural-tube defects have a lower recurrence rate if a daily 4-mg folic acid supplement is given.
During pregnancy, vitamin B12 levels are lower than nonpregnant values because of decreased levels of binding proteins, namely, the transcobalamins. During pregnancy, megaloblastic anemia is rare from deficiency of vitamin B12, that is, cyanocobalamin. Instead, a typical example is Addisonian pernicious anemia, which results from absent intrinsic factor that is requisite for dietary vitamin B12 absorption. his autoimmune disorder usually has its onset after age 40 years (Stabler, 2013).
In our limited experience, vitamin Bl2 deiciency in pregnancy is more likely encountered following gastric resection. hose who have undergone total gastrectomy require 1 000 �g of vitamin B12 given intramuscularly each month. Those with a partial gastrectomy usually do not need supplementation, but adequate serum vitamin B12 levels should be ensured (Appendix, p. 1258). Other causes of megaloblastic anemia from vitamin B12 deiciency include Crohn disease, ileal resection, some drugs, and bacterial overgrowth in the small bowel (Hesdorfer, 2015; Stabler, 2013).
Several conditions feature accelerated erythrocyte destruction. Damage may be stimulated by a congenital red-cell abnormality or in other cases by antibodies directed against red-cell membrane proteins. Hemolysis may be the primary disorder, and sickle-cell disease and hereditary spherocytosis are examples. In other cases, hemolysis develops secondary to an underlying condition such as systemic lupus erythematosus or preeclampsia. Microangiopathic hemolytic anemia due to malignancy has been reported in pregnancy (Happe, 2016).
he cause of aberrant antibody production is unknown. Typically, both the direct and indirect antiglobulin (Coombs) tests are positive. Anemias caused by these factors may be due to warm-active autoantibodies (80 to 90 percent), cold-active antibodies, or a combination. hese syndromes also may be classiied as primary (idiopathic) or secondary due to underlying diseases or other factors. Examples of the latter include lymphomas and leukemias, connective-tissue diseases, infections, chronic inlammatory diseases, and drug-induced antibodies (Provan, 2000). Cold-aglutinin disease may be induced by infectious etiologies such as Mycoplasma pneumoniae or Epstein-Barr viral mononucleosis (Dhingra, 2007). Hemolysis and positive antiglobulin test results may be the consequence of either immunoglobulin M (IgM) or immunoglobulin G (IgG) antierythrocyte antibodies. When thrombocytopenia is comorbid, it is termed Evans syndrome (Wright, 2013).