A 25-year-old woman, gravida 1 para 0, at 24 weeks gestation comes to the office due to diarrhea. The patient has intermittently loose stools 2-6 times a day. Bowel movements are always associated with lower abdominal cramps, which improve after defecation. Although the symptoms predate the pregnancy, they have worsened over the past few weeks. The patient denies constipation, fecal incontinence, hematochezia, melena, and vomiting. She has never experienced dysmenorrhea or painful intercourse. Her pregnancy has progressed without complication, and ultrasonography confirms that fetal size is appropriate for gestational age. Medical and family history are unremarkable, and the patient does not use tobacco or alcohol. Vital signs are within normal limits. Heart and lung sounds are normal. The abdomen is minimally tender to palpation in the bilateral lower quadrants without rebound or guarding. There is trace pitting edema in the bilateral lower extremities. Fecal occult blood testing is negative. Hemoglobin is 10.9 g/dL and mean corpuscular volume is 86 μm³. Erythrocyte sedimentation rate is normal. Which of the following most likely explains this patient's symptoms?

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11ec25c8_d270_13ff_bc81_510f76e336df_MD0003_00 Pregnancy induces a variety of physiologic changes that affect the gastrointestinal tract; an enlarging uterus and high levels of progesterone frequently cause constipation, hemorrhoids, gastroesophageal reflux, and biliary stasis. However, diarrhea is not a typical physiologic change in pregnancy, and this patient's intermittent diarrhea and abdominal pain that improves after defecation preceded her pregnancy, suggesting irritable bowel syndrome (IBS). IBS is characterized by recurrent abdominal pain (≥1 day/week for the past 3 months) related to defecation and is typically associated with abnormal bowel habits (eg, diarrhea and/or constipation). It is the most common gastrointestinal disorder and occurs most frequently in women age <45. As in this patient, symptoms often predate and are exacerbated by pregnancy. The evaluation of IBS is usually limited (eg, complete blood count, inflammatory markers, celiac serologies) and aimed at ruling out other diagnoses; those with alarm features typically require further evaluation with colonoscopy. Although iron deficiency anemia (ie, microcytic, hypochromic) is an alarm feature, this patient has a mild normocytic anemia consistent with physiologic, dilutional anemia of pregnancy (normal hemoglobin ≥10.5 g/dL in the second trimester), so colonoscopy is not indicated at this time. dilutional anemia of pregnancy (Choice A) Diverticulosis predisposes to gastrointestinal bleeding (eg, hematochezia, iron deficiency anemia) and diverticulitis (eg, left lower quadrant pain, fever, leukocytosis). Most patients with diverticulosis are elderly (eg, age >60), and pregnancy is not a typical risk factor. (Choice B) Endometriosis (implantation of endometrial tissue outside the uterus) often presents with recurrent lower abdominal pain, dysmenorrhea, dyspareunia, and infertility. Diarrhea is less common. (Choice C) Inflammatory bowel disease often flares during pregnancy, causing diarrhea, abdominal pain, and hematochezia. However, fecal occult blood is typically positive and elevated inflammatory markers (eg, erythrocyte sedimentation rate) would be expected. Although anemia is common, it is typically microcytic (due to iron deficiency). (Choice E) High levels of progesterone during pregnancy typically cause slowed colonic motility, resulting in constipation. The presence of diarrhea should prompt consideration of other etiologies such as IBS. Educational objective: Irritable bowel syndrome is characterized by recurrent abdominal pain (≥1 day/week for the past 3 months) related to defecation and is typically associated with abnormal bowel habits (eg, diarrhea and/or constipation). Symptoms often precede and are exacerbated by pregnancy. Laboratory evaluation (eg, complete blood count, inflammatory markers) is typically normal, and pregnant patients with an appropriate dilutional (normocytic) anemia do not require colonoscopy. References: Constipation in pregnancy: prevalence, symptoms, and risk factors. (http://www.ncbi.nlm.nih.gov/pubmed/18055731) Epidemiology and risk factors of functional constipation in pregnant women. (http://www.ncbi.nlm.nih.gov/pubmed/26208169)

A 25-Year-Old Woman, Gravida 1 Para 0, at 24 Weeks