A 21-year-old healthy woman, who is in week 34 of a normal pregnancy, complains of itching with burning pain in the perianal region for the past 4 months. She noted a small amount of bright red blood on toilet paper last week. Which of the following underlying conditions is most likely to be present in this patient?

The hemorrhoidal veins can become dilated from venous congestion. They are derived from ectoderm, covered by squamous epithelium, and innervated by somatic sensory nerves. External hemorrhoids are most common in patients with chronic constipation, but a pregnant uterus presses on pelvic veins to produce similar congestion, which promotes hemorrhoidal vein dilation. Filarial infections can affect lymphatics, including those in the inguinal region, and produce lymphedema. Polyarteritis does not affect veins. Portal hypertension with cirrhosis is most likely to dilate submucosal esophageal veins, but internal hemorrhoidal veins occasionally can be affected. Cirrhosis would be rare at this patient's age. Carcinomas are also uncommon at this age, and they are not likely to obstruct venous flow.