Case 6 – A 29-year-old pregnant woman seeking nutritional advice

A 29-year-old G2P1 woman presents to her obstetrician’s office at 10 weeks’ gestation for her screening visit. She reports no complaints and states that she has been feeling well. Her past medical history is significant for a seizure disorder that began when she was a teenager. Her seizures have been well controlled with phenytoin, and she was able to discontinue her medication during her previous pregnancy without incident. Since discovering she was pregnant again, she self-discontinued her medication and has been feeling well with no reported seizure activity. She is concerned about maintain an adequate nutritional intake during her current pregnancy.

What is the most important vitamin for this patient to take?

All women of child-bearing age are advised to consume a daily intake of 400 µg of folic acid throughout the periconceptional period to help prevent congenital neural tube defects. This patient’s history of anti-epileptic medication puts her fetus at greater risk for neural tube malformations, and so this patient is advised to ingest at least 4 mg of folic acid daily.

What is the mechanism of action of this vitamin?

Folic acid, a biochemically inactive compound, is the precursor for tetrahydrofolic acid and methyltetrahydrofolate, compounds that are essential for the maintenance of normal erythropoiesis and required cofactors for the synthesis of purine and thymidylate nucleic acids.

What vitamin should be avoided during pregnancy?

Vitamin A, also known as retinoic acid, is frequently used to treat severe cystic acne. Vitamin A should be avoided during pregnancy because of its association with spontaneous abortion and neural tube defects. Although vitamin A is most teratogenic when taken at 5-7 weeks’ gestation, it should be avoided at all gestational ages.

When is iron supplementation required in pregnancy?

Pregnancy causes a physiologic anemia. This is the result of the physiologic increase in plasma volume, which results in an effective decrease in hemoglobin and hematocrit. All pregnant women should take a daily prenatal vitamin that contains iron in order to avoid worsening anemia. Additional iron supplementation at higher doses should be given to any woman with a superimposed cardiac or hematologic condition, such as sickle cell disease.

What vitamin supplements must be given with iron?

When iron is given in large doses, as in the treatment for anemia, copper and zinc should also be prescribed, since large doses of iron inhibit the absorption of these minerals.

By Hindi Stohl Posy, MD, Resident in Obstetrics and Gynecology, Johns Hopkins University; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.