A 36-year-old woman, gravida 2 para 1, at 9 weeks gestation comes to the office to initiate prenatal care. The patient's first pregnancy ended in a vaginal delivery after an induction of labor at 37 weeks gestation for preeclampsia without severe features. She is otherwise healthy, and her only medication is a prenatal vitamin. The patient does not use tobacco, alcohol, or illicit drugs. Blood pressure is 120/70 mm Hg. BMI is 23 kg/m2. Pelvic ultrasound shows an intrauterine pregnancy at 9 weeks gestation with a normal heart rate. Prenatal laboratory tests to be drawn include a complete blood count, basic metabolic panel, urinalysis, and urine culture. Which of the following would be considered a normal finding in this patient?
Renal & urinary changes in normal pregnancy | |
Physiologic changes |
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Laboratory findings |
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BUN = blood urea nitrogen. | |
In pregnancy, both cardiac output and blood volume increase because the cardiovascular system adapts to rising metabolic demands and prepares for expected blood loss from delivery. As a result, other maternal organ systems also adapt and compensate with physiologic changes in pregnancy.
The maternal renal system experiences greater renal blood flow (perfusion) and individual glomeruli filter greater volumes of plasma (ie, increased glomerular filtration rate). Maternal production of blood urea nitrogen and creatinine stays relatively constant; however, due to the increased glomerular filtration rate, measured serum levels are decreased. A serum creatinine of 1.2 mg/dL, for example, may be the upper limit of normal in a nonpregnant patient but represents marked renal insufficiency in a pregnant patient (normal: 0.4 to 0.8 mg/dL). An additional renal adaptation in pregnancy is greater renal basement membrane permeability, resulting in increased urinary protein excretion.
Due to the increase in renal function during pregnancy, patients on medications that are renally excreted require close monitoring and dose adjustments as necessary.
(Choice A) Pregnancy is associated with leukocytosis, possibly due to inflammation. However, marked bandemia or elevated lymphocyte counts are abnormal and require further workup.
(Choice C) Increased, not decreased, urinary protein excretion of up to 300 mg/day occurs in pregnancy due to increased renal basement membrane permeability. Therefore, urine dipsticks positive for trace protein are normal in pregnancy.
(Choice D) During pregnancy, total blood volume expands. However, plasma volume increases out of proportion to red blood cell mass, causing a mild physiologic decrease in hemoglobin concentration. Laboratory definitions for anemia vary by trimester: <11 g/dL in the first and third trimesters and <10.5 g/dL in the second trimester. This dilutional anemia protects the mother in case of postpartum hemorrhage.
(Choice E) Platelet counts are typically normal or decreased, not increased, in pregnancy. Some patients acquire gestational thrombocytopenia (<100,000/mm3 but >70,000/mm3), which does not require further evaluation because it spontaneously resolves after delivery.
Educational objective:
In pregnancy, the cardiovascular system adapts to growing metabolic demands and prepares for expected blood loss from delivery by increasing cardiac output and blood volume. As a result, normal renal adaptations in pregnancy include increased renal blood flow, glomerular filtration rate, and urine protein excretion. These changes result in a physiologic decrease in serum blood urea nitrogen and creatinine.