Abdominal pain in a pregnant woman

True danger: Delay

Acute appendicitis is the most common condition requiring surgery during pregnancy.² Suspected appendicitis is the reason for nearly two thirds of all nonobstetric exploratory laparotomies performed during pregnancy; most cases occur in the second and third trimesters.

The incidence of appendicitis is 0.4 to 1.4 per 1,000 pregnancies.² Although the incidence of appendicitis is not greater during pregnancy, rupture of the appendix occurs 2 to 3 times more frequently in pregnancy due to delays in diagnosis and operation. Maternal and perinatal mortality and morbidity rates are greatly increased when appendicitis is complicated by peritonitis.

Why diagnosis is not so easy

Many symptoms of appendicitis are considered normal during pregnancy. For example, many times, pain in the right lower quadrant of the abdomen may be attributed to round ligament pain or urinary tract infection.

Anatomy. After the first trimester, the appendix is gradually displaced above McBurney’s point, with horizontal rotation of its base. This upward displacement occurs until the eighth month of gestation, when more than 90% of appendices lie above the iliac crest, and 80% rotate upward and toward the right subcostal area.^2,3

Symptoms. The most consistent clinical symptom encountered in pregnant women with appendicitis is vague right-sided abdominal pain.²

• Depending on the gestation, muscle guarding and rebound tenderness may or may not be present.
• Nausea, vomiting, and anorexia are usually present as in the nonpregnant patient.
• Twenty-five percent of pregnant patients with appendicitis are afebrile, as our patient was.^2,4
• The leukocytosis of pregnancy makes it difficult to determine if there is an infection. Not all pregnant patients with appendicitis have a white blood cell count of more than 16,000/mL, but approximately 75% have a left shift in the differential.² Urinalysis may reveal pyuria and hematuria, and can mislead the physician, who may attribute the symptoms to pyelonephritis.²

How likely is fetal loss?

Fetal loss may occur with preterm labor and delivery or with generalized peritonitis and sepsis, but occurs only rarely in uncomplicated appendicitis. Fetal loss appears to be more closely linked to severity of appendicitis than to surgical intervention.^2,5,6

Graded compression ultrasonography vs CT

It is imperative that any pregnant patient who comes to the hospital with abdominal pain be evaluated for appendicitis. Ultrasound was a valuable diagnostic tool in this case and saved both the patient and developing fetus the radiation exposure of a CT scan. Ultrasound has a high specificity for diagnosing appendicitis if the appendix is visualized with abnormal findings. However, the sensitivity is not as high as CT (TABLE),⁷ and failure to visualize the appendix adequately would have required a decision between appendectomy on clinical grounds or going ahead with the CT scan.

A prospective study of patients with signs and symptoms of acute appendicitis found that the graded compression ultrasonography technique was as accurate as focused unenhanced single-detector helical CT. The primary sonographic criterion for the diagnosis was an incompressible appendix with a transverse outer diameter of 6 mm or larger, as seen in this patient. The sensitivity of CT and sonography was 76% and 79%, respectively; the specificity was 83% and 78%; the accuracy was 78% and 78%; the positive predictive value was 90% and 87%; and the negative predictive value was 64% and 65%.⁸

A rational strategy

It is reasonable to use graded compression ultrasonography in a pregnant woman with suspected appendicitis. If suspicion for appendicitis is high, a negative result may still need further evaluation with a CT or ultimately lead to abdominal surgery despite negative imaging studies.

TABLE

Predictive values of ultrasound and CT in the diagnosis of appendicitis

This article is adapted from Muñoz M, Usatine RP. Abdominal pain in a pregnant woman. J Fam Pract. 2005;54:665-668.