View source for WBR0194

{{WBRQuestion
|QuestionAuthor=Mahmoud Sakr M.D.
|ExamType=USMLE Step 2 CK
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|MainCategory=Internal medicine
|MainCategory=Internal medicine
|SubCategory=Allergy/Immunology, Cardiovascular, Respiratory
|Prompt=35 year-old pregnant female, 18 weeks gestation comes for a routine prenatal followup. She has no complaints except for mild pitting edema of her ankles. You order a set of labs which include renal functions, CBC and a thyroid profile. Which of the following will most likely appear on her lab work:
|Explanation=Maternal physiological changes in pregnancy are the normal adaptations that a woman undergoes during pregnancy to better accommodate the embryo or fetus. They are physiological changes, that is, they are entirely normal, and include cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications. 
During pregnancy the plasma volume increases by 50% and the red blood cell volume increases only by 20-30%.  Consequently, the hematocrit decreases on lab value; this is not a true decrease in hematocrit, however, but rather due to the dilution.
The glomerular filtration rate (GFR) commonly increases by 50%, returning to normal around 20 weeks postpartum, therefore there’s a decrease in blood urea nitrogen (BUN) and creatinine. TSH will be normal while total T3 and T4 may increase as a result of high estrogen levels.

|AnswerA=High TSH, low hematocrit and low BUN


|AnswerAExp=Low hematocrit and low BUN are correct, but TSH will be normal. 
|AnswerB=Low TSH, Low hematocrit and low BUN

|AnswerBExp=Low hematocrit and low BUN are correct, but TSH will be normal. 
|AnswerC=Normal TSH, low hematocrit and low BUN

|AnswerCExp=This is the correct answer as explained in the overall explanation.
|AnswerD=Normal TSH, high hematocrit and high BUN

|AnswerDExp=Hemodilution and increased GFR associated with pregnancy leads to low values of BUN and Creatinine.
|AnswerE=Normal TSH, normal hematocrit, normal BUN
|AnswerEExp=Hemodilution and increased GFR associated with pregnancy leads to low values of BUN and Creatinine.
|RightAnswer=C
|Approved=Yes
}}