A 23-year-old primigravida at 18 weeks gestation presents to the clinic for a routine prenatal visit. She reports feeling well and has no complaints. Vital signs are within normal limits. A comprehensive metabolic panel is obtained as part of her evaluation. The results show a blood urea nitrogen (BUN) level of 7 mg/dL and a serum creatinine level of 0.4 mg/dL. Urinalysis reveals no protein or blood. Which of the following physiological adaptations of pregnancy is the most likely cause of these laboratory findings?
- Increased glomerular filtration rateAnswer
- BPhysiologic hemodilution
- CDecreased hepatic synthesis of urea
- DIncreased renal tubular reabsorption
- EDecreased skeletal muscle mass
Answer
Increased glomerular filtration rate
The correct answer accurately identifies that a normal physiological change during pregnancy is a substantial increase in renal plasma flow and glomerular filtration rate (GFR). This increase can be up to 50% above non-pregnant levels. As a result, the renal clearance of urea and creatinine increases, leading to naturally lower baseline serum levels of blood urea nitrogen (BUN) and creatinine (e.g., BUN < 10 mg/dL, creatinine < 0.8 mg/dL) compared to non-pregnant patients. Recognizing these lowered values as normal is crucial to avoid unnecessary and potentially harmful diagnostic workups.
Step-by-Step Solution
Key Concept
During normal pregnancy, renal blood flow and glomerular filtration rate (GFR) increase significantly, leading to decreased baseline serum levels of BUN and creatinine.