1. Regarding routine testing in normal pregnancy, which one of the following pairs is an incorrect match?
A. First trimester screen (free β-hCG, PAPP-A)/Assessment for Down syndrome
B. Glucose/Assessment for gestational diabetes mellitus
C. Treponemal antibody test/Assessment for group B Streptococcus to prevent transmission to fetus during delivery
D. Second trimester “quad” screen (hCG, AFP, estriol, inhibin A)/Assessment for Down syndrome, neural tube defects, and other fetal anomalies
The correct answer is C. The treponemal antibody test is to screen for syphilis, and not group B streptococcal infection. A group B Streptococcus cervical culture is important in the third trimester. If the test is positive, treatment is provided to prevent transmission to the fetus during delivery.
2. Pregnancy causes alterations in many laboratory tests such that the reference ranges are different during pregnancy. Which one of the following shows an incorrect change in the reference range during pregnancy?
A. Hematocrit is increased
B. Alkaline phosphatase activity is increased
C. 1,25-dihydroxyvitamin D is increased
D. Total T3 and T4 are increased
The correct answer is A. The hematocrit is decreased during pregnancy because there is an increase in the plasma volume. For that reason, the percentage of red cells relative to the entire blood volume is decreased. Alkaline phosphatase activity is increased due to the production of placental, heat-stable alkaline phosphatase. 1,25-Dihydroxyvitamin D is increased as a result of increased calcium and transfer of calcium to the fetus. Total T3 and T4 are increased, but the patient remains euthyroid.
3. Depending on the assay, 2 to 5 IU/L, a detectable amount of hCG, is present in the serum how many days after conception?
The correct answer is D. An increase in hCG, when measured with a quantitative assay and a serum sample, is detectable 8 to 11 days after conception. On the other hand, qualitative urine hCG tests (that produce a yes or no answer) have detection limits that range from 20 to 50 IU/L and become positive 14 or more days after conception, usually after a missed menstrual period.
4. For the first 8 weeks of pregnancy, hCG doubles every how many days until it reaches a peak between 100,000 and 500,000 IU/L?