A -year-old gravida , para at weeks gestation presents to the clinic for a scheduled prenatal evaluation. She reports mild shortness of breath when walking up stairs and increased urinary frequency over the past few weeks, but otherwise feels well. Her first pregnancy was uncomplicated, resulting in a term vaginal delivery. Vital signs show a blood pressure of mm Hg, heart rate of /min, and respiratory rate of /min. Physical examination reveals a gravid uterus consistent with gestational age and trace bilateral pedal edema. Laboratory studies reveal the following:
| Laboratory Study | Result |
|---|---|
| Hemoglobin | g/dL |
| Sodium | mEq/L |
| Creatinine | mg/dL |
| Arterial blood gas (room air) | |
| pH | |
| PaCO | mm Hg |
| PaO | mm Hg |
| HCO | mEq/L |
| Urinalysis | |
| Protein | Trace |
| Glucose | |
| Leukocyte esterase | Negative |
Which of the following is the most appropriate next step in the management of this patient?
- Administer a -g oral glucose load and measure serum glucose in hourAnswer
- BObtain a -hour urine collection for total protein and creatinine clearance
- CPerform a lower extremity compression ultrasonography
- DProceed directly to a -hour -g oral glucose tolerance test
- EInitiate fluid restriction and monitor serum sodium levels
Answer
The correct approach is to proceed with standard prenatal screening by administering a 50-g oral glucose load and measuring serum glucose in 1 hour.
This patient's clinical presentation and laboratory findings represent the normal physiological adaptations of pregnancy across multiple organ systems. Progesterone stimulates the respiratory center, leading to hyperventilation and a primary respiratory alkalosis (low PaCO2) with metabolic compensation (low HCO3-). Plasma volume expansion outpaces red blood cell mass production, causing dilutional anemia (hemoglobin >10.5 g/dL is normal in the second trimester). The glomerular filtration rate increases by approximately 50%, which decreases serum creatinine (normal in pregnancy is 0.4-0.8 mg/dL) and often exceeds the proximal tubule's reabsorptive capacity for glucose, leading to benign glucosuria. Furthermore, the resetting of the osmostat by human chorionic gonadotropin and relaxin results in a mild, asymptomatic hyponatremia (typically 130-132 mEq/L). Because all of her findings are strictly physiological, she requires only routine prenatal care. Between 24 and 28 weeks gestation, all pregnant women undergo universal screening for gestational diabetes mellitus. The standard initial step is the 1-hour 50-g oral glucose challenge test.
Step-by-Step Solution
Key Concept
Recognizing the broad spectrum of normal maternal physiological adaptations to prevent unnecessary workups, while adhering to the standard second-trimester prenatal screening schedule.