Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (272 page)

   
Iron studies
: Serum iron decreases 40% in women not on iron therapy. Serum vitamin B
₁₂
level decreases 20%. Serum folate decreases ≥50%. Overlap of decreased and normal range of values often makes this test useless in diagnosis of megaloblastic anemia of pregnancy. Serum transferrin increases 40% and percent saturation decreases ≤70%. Serum ceruloplasmin increases 70%.

   Laboratory Monitoring of Pregnancy

At the first prenatal visit,
all pregnant women should receive the following:

   Pap test if not done in preceding year to rule out dysplasia.

   CBC to rule out hematologic abnormalities (may be suggestive of genetic disorders such as thalassemia or iron deficiency or B
₁₂
/folate deficiency anemia).

   Blood type, Rh type, and antibody screen.

   Rubella screen, rapid plasma reagin (RPR) test, or syphilis antibody EIA test; HBsAg and HIV test should be offered.

   For high-risk women, test for
N. gonorrhoeae, C. trachomatis
, and HBsAg; repeat at 28 weeks.

   For women with diabetes during pregnancy, obtain a hemoglobin A1c.

First trimester
(10w3d and 13w6d) testing may include the following:

   Maternal triple screen (pregnancy-associated placental protein A (PAPP-A), total hCG, and ultrasound for nuchal translucency and genetic diseases; optimally drawn between 11 and 13 weeks 6 days)
OR

   Serial sequential testing with combined sonography and maternal serum testing for PAPP-A in first trimester followed with testing for PAPP-A, AFP, hCG, unconjugated estriol, and dimeric inhibin A in the second trimester. The first trimester specimen must be drawn between 11 and 18 weeks’ gestation and the second specimen drawn between 15 and 22 weeks’ gestation.

   Genetic testing for CF and other familial diseases should be offered (see Chapter
10
).

   Cell-free DNA testing (noninvasive prenatal testing, NIPT) for trisomies 21, 18, and 13 and monosomy X may be considered for high-risk patients and may be drawn as early as 9 weeks of gestation.