A 38-year-old woman, gravida 1 para 0, at 34 weeks gestation comes to the office due to increasing swelling in her hands and legs. The patient first noticed the swelling a few weeks ago but now cannot stand for more than an hour without needing to elevate her legs. She has no orthopnea, dyspnea, or chest pain. The patient has no chronic medical conditions and takes no daily medications. Vital signs are normal. Cardiac examination is within normal limits. Lungs are clear to auscultation. Bilateral lower extremities have 2+ pitting edema to the midshin. Urine dipstick shows no protein. Compared to a healthy nonpregnant woman, which of the following parameters is most likely to be decreased in this patient?

Question

A 38-year-old woman, gravida 1 para 0, at 34 weeks gestation comes to the office due to increasing swelling in her hands and legs.  The patient first noticed the swelling a few weeks ago but now cannot stand for more than an hour without needing to elevate her legs.  She has no orthopnea, dyspnea, or chest pain.  The patient has no chronic medical conditions and takes no daily medications.  Vital signs are normal.  Cardiac examination is within normal limits.  Lungs are clear to auscultation.  Bilateral lower extremities have 2+ pitting edema to the midshin.  Urine dipstick shows no protein.  Compared to a healthy nonpregnant woman, which of the following parameters is most likely to be decreased in this patient?

Quizplus · Accepted Answer

11ec160b_3cd7_7fe3_9249_b765f7087828_MD0001_00 During pregnancy, the maternal cardiovascular system undergoes physiologic adaptations to increase cardiac output and optimize fetal perfusion. The most significant hemodynamic change is a marked decrease in systemic vascular resistance (SVR), which occurs due to increased release of peripheral vasodilators (eg, nitric oxide, prostacyclin) and decreased vascular sensitivity to vasoconstrictors (eg, norepinephrine, angiotensin II). The formation of a high-flow, low-resistance circuit within the uterus and placenta also contributes to decreased SVR. Decreased SVR induces mild hypotension, which along with direct stimulation by placental hormones, leads to activation of the renin-angiotensin-aldosterone system. This results in fluid retention and an increase in plasma blood volume of up to 40% in pregnancy (Choice D). This physiologic increase in plasma blood volume inevitably results in increased venous return (ie, increased cardiac preload), which together with reduced SVR (ie, decreased cardiac afterload) facilitates a greater stroke volume and increased cardiac output (Choices A and B). Pulmonary vascular resistance (PVR) also decreases during pregnancy, likely via the same vasodilatory mechanisms as SVR. This helps accommodate the increased preload to the right heart while maintaining a normal central venous pressure (CVP) (Choice C). Vascular capacitance (ie, the ability of systemic veins to stretch) also helps accommodate increased total blood volume without affecting the CVP. Despite normal CVP, peripheral edema is common in pregnancy due to the increase in plasma volume resulting in decreased blood oncotic pressure; this change encourages leakage of intravascular fluid into dependent peripheral tissue (eg, lower extremities). Educational objective: During pregnancy, systemic vascular resistance decreases and plasma blood volume increases. Venous capacitance and a decrease in pulmonary vascular resistance allow for accommodation of increased blood volume without affecting central venous pressure (CVP). Despite a normal CVP, peripheral edema is common in pregnancy due to decreased capillary oncotic pressure that encourages leakage of fluid into dependent peripheral tissues (eg, lower extremities).

A 38-Year-Old Woman, Gravida 1 Para 0, at 34 Weeks