Acute Abdominal Pain in Pregnancy

Kelly A. Best

Acute abdominal pain in pregnancy poses a unique challenge for both the clinician and the patient. The physiologic and physical changes associated with pregnancy must be considered when conducting a history, performing a physical examination, and interpreting diagnostic and other laboratory results in the pregnant patient with acute abdominal pain.

This chapter reviews common causes of acute abdominal pain in pregnancy and facilitates interpretation of laboratory and diagnostic tests in pregnant women. The diagnostic approach to pregnant as well as nonpregnant patients should be similar. Clinicians should resist the temptation to uniformly attribute the patient’s symptoms to her pregnancy. In addition, clinicians should have a high index of suspicion as classical findings may not be present for certain dis­ease states. Delay in diagnosis resulting in complications associated with the underlying condition may lead to premature labor and delivery (3).

PHYSIOLOGIC CHANGES IN PREGNANCY

Expansion of the plasma volume and an increase in red blood cell mass begin as early as the 4th week of pregnancy, peak at 28 to 34 weeks of gestation, and then plateau until parturition (4,5). Plasma volume expansion is accompanied by a lesser increase in red cell volume (6). As a result, there is a modest reduction in hematocrit, with peak hemodilution occurring at 24 to 26 weeks.

During pregnancy, white cell volume increases from 5,000 to 6,000 cells/ mm³ to 16,000 cells∕mm³ in the second and third trimesters and to 20,000 to 30,000 cells∕mm³ in early labor (9). The glomerular filtration rate (GFR) and renal blood flow rise markedly during pregnancy. The increase in GFR can be demon­strated within 1 month of conception and reaches a peak approximately 40% to 50% above baseline levels by the end of the first trimester, resulting in a decrease in blood urea nitrogen and serum creatinine as well as glucosuria despite nor­mal plasma glucose levels (10). Both kidneys increase in size by 1 to 1.5 cm during pregnancy primarily due to an increase in renal vascular and interstitial volumes (10). Ureteral dilatation during pregnancy results from hormonal effects, exter­nal compression, and intrinsic changes in the ureteral wall (11). Physiologic hydronephrosis typically occurs and is more common on the right than the left side (90% versus 10%).

In the respiratory system, the diaphragm rises by up to 4 cm, and the chest diameter can increase by 2cm or more (12). Diaphragmatic excursion is not limited by the uterus and actually increases by up to 2 cm. Pregnancy is a state of relative hyperventilation, which may be centrally mediated through progester­one. The respiratory rate does not change while the tidal volume increases, resulting in an approximately 50% increase in minute ventilation. The normal PaO2 in pregnant women ranges from 100 to 110 mm Hg (13-16). In addition, there is a decrease in arterial carbon dioxide levels (PCO2 and PaCO2) from the nonpregnant average of 40 mm Hg to a plateau of 27 to 32 mm Hg during preg­nancy (14,15).

Physical examination changes in pregnancy

Pain perceived from the abdomen is caused by peritoneal irritation, mechanical stretching, or ischemia (17). Physical exam findings in pregnancy may be blunted compared with those of nonpregnant patients with the same disease or process. Peritoneal signs may be absent due to the lifting and stretching of the anterior abdominal wall in pregnancy, preventing contact with the parietal peritoneum and eliminating rebound tenderness or guarding (18). In addition, the gravid uterus may distort the clinical picture by obstructing the movement of the omen­tum to an area of inflammation. Performing an examination with a pregnant patient in the left or right decubitus position, displacing the uterus to one side, may be of some benefit in certain clinical situations.

IMAGING TECHNIQUES

Diagnostic imaging is often necessary during pregnancy. Sonographic examina­tion is a common occurrence in pregnant women, but other types of radiological evaluation may also be required. Although the safety of radiation exposure dur­ing pregnancy is a common concern, a missed or delayed diagnosis can pose a greater risk to the woman and her pregnancy than any hazard associated with ionizing radiation (19). In many cases, the perception of fetal risk is higher than the actual risk (20,21). Table 2.1 provides an overview of the total fetal exposure of ionizing radiation in some commonly performed radiologic studies. Ionizing radiation can result in the following three harmful effects: (a) cell death and teratogenic effects, (b) carcinogenesis, and (c) genetic effects or mutations in germ cells (22). The threshold at which an increased risk of congenital malforma­tions is observed in radiation-exposed embryos/fetuses has not been definitively determined.

Women should be counseled that X-ray exposure from a single diagnostic proce­dure does not result in harmful fetal effects. Specifically, exposure to less than 5 rad has not been associated with an increase in fetal anomalies or pregnancy loss.

Concern about possible effects of high-dose ionizing radiation exposure should not prevent medically indicated diagnostic X-ray procedures from being per­formed on a pregnant woman. During pregnancy, other imaging procedures not associated with ionizing radiation (ultrasonography, MRI) should be considered instead of X-rays when appropriate.

Note: 1 rad = 0.01 gray (Gy).

Source: Adapted from Ref. 24; Data from Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC III, Hauth JC,

Wenstrom KD (eds). General considerations and maternal evaluation. In: Williams Obstetrics. 21st Ed. New York, NY: McGraw-Hill; 2001:1143-1158.

COMMON CAUSES OF ACUTE ABDOMINAL PAIN IN PREGNANCY

The differential diagnosis of acute abdominal pain in pregnancy includes etiologies similar to those in the nonpregnant patient as well as causes specific to the pregnancy (Table 2.2). The following sections review common causes of acute abdominal pain in pregnancy and detail safe diagnostic strategies for both the mother and the fetus.

Appendicitis

Acute appendicitis is the most common nonobstetric surgical diagnosis during pregnancy (25). The incidence ranges from 0.06% to 0.1%, or 1 in 1,500 deliveries (26-28). Appendicitis is more frequently seen in the second trimester when com­pared with the first and third trimesters or during the postpartum period (29).

Right lower quadrant pain is the most common symptom of appendicitis. Although older studies suggested that the location of the appendix migrates upward with the enlarging uterus, this theory has been refuted by subsequent stud­ies which have found that the most common symptom of appendicitis, that is, right lower quadrant pain, occurs within a few centimeters of McBurneys point in the vast majority of pregnant women, regardless of the stage of pregnancy (31,32).

The physiologic changes of pregnancy can confound the diagnosis of appen­dicitis. Leukocytosis can be a normal finding in pregnant women. Indigestion, bowel irregularity, nausea/vomiting, as well as a sense of not feeling well are also common symptoms of both appendicitis and normal pregnancy. The temporal relationship of these symptoms is essential in differentiating early appendicitis from the nausea and vomiting of pregnancy. In appendicitis, nausea and vomit­ing, if present, typically follow the onset of pain, whereas nausea and vomiting associated with pregnancy are not usually associated with pain. Microscopic hematuria and pyuria are found in up to one third of patients with acute

appendicitis, and a decrease in the direct contact between the area of inflamma­tion and the parietal peritoneum results in less muscle response or guarding.

The gold standard for diagnostic imaging of the appendix in pregnancy is graded compression ultrasonography. Appendicitis is diagnosed if a noncom- pressible blind-ended tubular structure is visualized in the right lower quadrant with a maximal diameter >6 mm (33,34). Magnetic resonance imaging (MRI) can be useful for the next step in cases with diagnostic uncertainty and provides an attractive alternative to CT because it avoids exposure to ionizing radiation.

Consultation with a general surgeon should be obtained in women whose imaging studies or physical examination suggest appendicitis. The decision to proceed to laparotomy should be based upon the clinical findings, the diagnostic imaging results, and the clinical judgment. Given the diagnostic difficulties and the significant risk of fetal morbidity or mortality with perforation (36% versus 1.5%) (26) or with peritonitis or abscess (fetal loss: 6% versus 2%; early delivery: 11% versus 4%), a higher negative laparotomy rate (20% to 35%) compared with nonpregnant women has generally been considered to be acceptable (35,36).

A transverse incision at McBurneys point, or more commonly over the point of maximal tenderness, can be utilized in pregnancy (37). When the diag­nosis is less certain, a lower midline vertical incision can be utilized since it per­mits adequate exposure of the abdomen for diagnosis and treatment of surgical conditions that mimic appendicitis. A vertical incision can also be used for a cesarean delivery, if subsequently required for obstetric indications. Case reports and small case series regarding laparoscopic appendectomy in pregnancy sug­gest that such procedures can be performed successfully during all trimesters and with few complications (38-41). The decision to proceed with such an approach should take into consideration the skill and experience of the surgeon, as well as clinical factors such as the size of the gravid uterus. Modifications of the technique during pregnancy should include the following: a slight left lateral positioning of the patient, avoiding the use of any cervical instruments; use of open entry techniques or placement of trocars under direct visualization; and limiting the intra-abdominal pressure to throughout pregnancy, while surgical management of complicated adnexal masses is necessary in approximately 1 in 1,300 pregnancies (51,52).

Adnexal torsion is more common in pregnancy than in the nonpregnant state (26) and has been reported in up to 7% of pregnant patients with adnexal masses (53). Pain associated with torsion is often intermittent, crampy and may radiate to the ipsilateral thigh or flank. Nausea and vomiting may also develop. Examination findings may include a palpable fullness in the pelvis or lower quad­rant and, in the presence of rupture, peritoneal signs may be present. While the patient may remain afebrile with a normal or slightly elevated white count, hemo­globin may be decreased when rupture results in hemoperitoneum (and in severe cases, hypovolemic shock). Transvaginal and transabdominal ultrasound exami­nations are the imaging modalities of choice when evaluating an adnexal mass.

While laparotomy (with a vertical midline incision to facilitate exposure and allow for extension if indicated) should be regarded as the preferred approach for the surgical management of ovarian torsion in pregnancy, several reports have suggested that laparoscopy by a surgeon skilled in this approach may be acceptable (53-55). In some circumstances, adnexal cyst rupture may be treated expectantly if the clinical condition remains stable.

A persistent adnexal cyst larger than 5 cm in a pregnant woman should be removed electively during the early second trimester of pregnancy because tor­sion, rupture, or hemorrhage often requires emergency surgery and can lead to preterm delivery (51). On occasion, a simple cyst that is 5 to 10 cm in size can be managed expectantly if the patient is asymptomatic and serial ultrasound exam­inations show no increase in size. If the cyst persists, excision can be performed at cesarean delivery or postpartum. It is important to consider that a large adn­exal cyst in the posterior cul-de-sac has the potential to produce obstructed labor and delivery. Surgical intervention is indicated for an adnexal mass of any size suspicious for malignancy or if torsion, rupture, or hemorrhage is suspected. An adnexal mass identified incidentally at the time of cesarean delivery should be removed (56). Complete surgical removal is preferred to aspiration since malignancy could be missed even with simple, smooth-walled cysts (57).

Postoperative progesterone is recommended when the corpus luteum is removed prior to 8 to 10 weeks of gestation.

Pyelonephritis and Nephrolithiasis

Acute pyelonephritis is a common complication of pregnancy as the physiologic changes in pregnancy often predispose women to this condition. Ascending infection from the urinary bladder is the likely etiology in the majority of cases. As the gravid uterus enlarges, increased pressure on the ureters at the pelvic brim, as well as the relaxant effect of circulating progesterone on the ureters, predisposes the pregnant patient to urinary stasis (58).

Patients with acute pyelonephritis often appear acutely ill and may com­plain of flank pain, dysuria, frequency, fever, and shaking chills. Costovertebral angle tenderness may be present on the affected side while abdominal pain is less common. The white count will likely be elevated with a concomitant left shift. Urinalysis typically reveals both pyuria and bacteriuria. Urine culture with sensitivity will guide treatment; however, initiation of intravenous antibiot­ics directed at Gram-negative enteric bacteria should be initiated as soon as pos­sible while urinary cultures are pending.

The development of symptomatic nephrolithiasis during pregnancy is a rare event, occurring in about 1 in every 1,500 to 3,000 pregnancies (59). Affected patients usually present in the second or third trimester (—20% in the first tri­mester) with acute flank pain (90%), which often radiates to the groin or lower abdomen. Nausea, vomiting, urinary frequency, and urgency are also typical. Microscopic hematuria is present in 75% to 95% of patients, one third of whom have gross hematuria (59).

Renal and pelvic ultrasound should be performed when an obstructing calculus is suspected. This modality avoids exposure to radiation and is useful for detecting secondary signs of obstruction, such as hydronephrosis or hydroureter (60). Physiologic hydronephrosis of pregnancy must be distinguished from patho­logical hydronephrosis from obstruction. When the ultrasound examination is negative and the patient has continued discomfort suggestive of nephrolithiasis, two options are available for diagnosis: a limited intravenous pyelogram (IVP) in which a single abdominal radiograph is taken approximately 5 minutes after intra­venous administration of contrast material (60) or, if available, ureteroscopy (61). The single-shot IVP, which delivers about 50 mrad to the fetus, is positive in most pregnant women with a symptomatic stone (60). MRI can also be a useful adjunct in assessing stones during pregnancy. T2-weighted MRI can offer differing urographic appearances in physiologic and calculus obstruction (62).

Most (75% to 85%) stones pass spontaneously, due in part to the normally dilated urinary tract in pregnant women (58,59). Cystoscopy with insertion of a ureteral stent or ureteroscopy to remove or fragment the stone may be required in the patient who is septic, has persistent severe pain, or has obstruction in a solitary functioning kidney (61,63). Ureteral stenting or placement of a neph­rostomy tube to relieve obstruction or pain is a valid option for managing preg­nant patients. However, pregnancy significantly increases the risk of stent encrustation, necessitating the need for frequent ureteral stent exchange (64). If conservative management fails, ureteroscopy with lithotripsy may be an option. Although shock wave lithotripsy has been inadvertently performed in a few pregnant women, its use during pregnancy is currently contraindicated (65,66).

Bowel Obstruction

Bowel obstruction complicates 1 in 1,500 to 3,500 deliveries (67). Risk factors for bowel obstruction in pregnancy are related to adhesions from pelvic infection and previous surgery, complications of Crohn’s disease, intussusception, and more rarely neoplasm.

Symptoms of intestinal obstruction are similar to those in the nonpregnant population and include abdominal distention, vomiting, abdominal pain, and an inability to pass flatus. Pain is generally periumbilical, paroxysmal, and crampy. On physical examination, the large, gravid abdomen may pose a diagnostic chal­lenge as it may mask the usual findings during auscultation, percussion, and palpation. In general, abdominal tenderness, abnormal bowel sounds (high pitched or hypoactive), tachycardia, and hypotension may be present.

While laboratory studies are not helpful in establishing the diagnosis of bowel obstruction, they may be utilized to monitor the white blood cell count (a sharp rise over a short period of time may indicate strangulation) and to assess the degree of dehydration. The diagnosis of small bowel obstruction can be made by a history and a physical examination in the majority of patients. Plain abdominal radiogra­phy is used to confirm the diagnosis of bowel obstruction. Ordering an upright chest film to rule out the presence of free air, as well as supine and upright abdom­inal films, is appropriate in this setting. Of note, plain films can be equivocal in 20% to 30% of patients and are “normal, nonspecific, or misleading” in 10% to 20% (68,69). Multiple air-fluid levels with distended loops of small bowel are seen in small bowel obstruction, although occasionally they can be seen in the setting of a paralytic ileus. Abdominal ultrasonography can also be useful, especially as a bedside test for the critically ill (70,71).

Treatment of small bowel obstruction in pregnancy is similar to that in nonpregnant individuals. Aggressive intervention is warranted because delay in treatment increases maternal and fetal morbidity and mortality. Fluid and elec­trolyte replacement, bowel decompression, and prompt surgical intervention in cases resistant to decompression are suggested.

LAPAROSCOPIC SURGERY IN PREGNANCY

Laparotomy has generally been accepted as the approach of choice for surgical exploration in pregnancy. Recent case reports and case series of successful laparos­copy in pregnancy have called into question this long-held belief (55,72,73). Theoretical areas of concern have included the potential decrease in uteroplacental blood flow resulting in fetal hypoxia due to the rise in intra-abdominal pressure dur­ing pneumoperitoneum, fetal acidosis from absorption of carbon dioxide, and direct or indirect fetal injury if the uterus is perforated by a trocar or a Veress needle.

Although prospective studies are lacking, multiple case series evaluating the safety of laparoscopy in pregnancy have reported laparoscopic procedures in all trimesters with minimal morbidity to the fetus with regard to fetal weight, gestational duration, intrauterine growth restriction, congenital malforma­tions, stillbirths, or neonatal deaths (73).

The benefits of laparoscopy for pregnant and nonpregnant women include less postoperative pain, less postoperative ileus, reduction in adhesion formation, shorter hospital stay, less narcotic use, improved respiratory efforts, and faster return to usual activities (74). In addition, there may be less uterine manipulation and improved visu­alization in the gravid population when compared with laparotomy (73-75). The fol­lowing are considerations when laparoscopy is performed in pregnancy:

1. Laparoscopy can be performed in any trimester; however, the optimal time for nonemergent indications is the early second trimester.

2. Use of an oral or nasogastric tube for gastric decompression.

3. Use of prophylactic pneumatic compression devices (with the need for pharmacologic thromboprophylaxis determined on a case-by-case basis) to prevent thrombosis.

4. Avoidance of uterine/cervical manipulators.

5. Supine or low lithotomy position with a leftward tilt.

6. Establishment of pneumoperitoneum is dependent on the surgeon’s experience and comfort.

7. Intra-abdominal pressure should be maintained between 8 and 12 mm Hg and should not exceed 15 mm Hg.

8. Fetal heart rate should be confirmed and documented before and after the procedure. If fetal monitoring is necessary during the pro­cedure, consideration for transabdominal or transvaginal ultra­sound assessment should be made.

9. Fetal heart rate and uterine activity should be monitored in the recov­ery room by protocols appropriate for gestational age.

10. Nonsteroidal antiinflammatory drugs should be avoided, especially after 32 weeks of gestation, while opioids and antiemetics can be used as needed.

SUMMARY

The presence of the fetus should not delay the decision to perform the indi­cated diagnostic testing or to initiate treatment, as delays in this setting often result in significant morbidity and mortality for both the mother and the fetus. A multidisciplinary approach with early consultation from obstet­ric, surgical, laboratory, and radiologic services is warranted. Because obstet­ric causes for abdominal pain exist in many patients, however, consultation with an obstetric provider will help to define the subset of patients who warrant further investigation into nonobstetric sources for acute abdominal pain.

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