Chapter 3: Maternal Physiology

Question 1

hCG is structurally similar to which protein? Which subunits are identical?

Answer 1

hCG is similar to TSH (thyrotropin)
a subunits are identical
B subunits differ in there amino acid sequence

effect: high hCG levels cause thyroid stimulation

Question 2

True or false:

1. TRH levels rise during pregnancy
2. TRH and TSH crosses the placenta.
3. Thyroid gland size remains unchanged.
4. TSH has direct fetal effects.

Answer 2

False. TRH levels DO NOT RISE.
True. TRH can cross the placenta. TSH cannot cross.
False. Thyroid gland enlarges (12mL 1st trimester to 15mL at term) to boost production of thyroid hormones by 40-100%.
False. TSH does not cross, so it has no direct fetal effects.

Question 3

What happens to the following during pregnancy (maternal)?

1. TBG
2. Total T4
3. FT4
4. TSH
5. Iodine requirements

Answer 3

TBG rises, reach zenith at 20wks, stabilize at approximately double the value. (due to increased liver synthesis and decreased metabolism)

Total T4 increased due to the increase in TBG. Rise sharply at 6-9weeks, plateaus at 18.

FT4 rises only slightly, peak with hCG then return to normal.

TSH is normally suppressed –> pregnant women are misdiagnosed as subclinical hyperthyroidism

Iodine requirements increase.

Question 4

When does the fetal thyroid:

1. begin to concentrate iodine?
2. begin to synthesize and secrete thyroid hormone by fetal pituitary TSH

Answer 4

1. 10-12weeks

2. 20weeks

Question 5

Maternal source account for ___ % of thyroxine in fetal serum at term.

Answer 5

30%