Abdominal pain is very much the home territory of the general surgeon. This review will apply a contemporary framework to the management of the pregnant patient with abdominal pain presenting in the second and third trimesters.

When a pregnant patient requires surgical consultation it may be in several different settings: the clinic, the emergency room, the intensive care unit or the operating theatre. Whatever the situation, it mandates a team approach, where surgeons, obstetricians, anaesthetists, paediatricians and, occasionally, radiologists have to work closely together to provide the best care for mother and fetus. Moreover, time is often the enemy of a good result. Diagnosis should be prompt and treatment, including surgical treatment, should not be delayed.

Ectopic pregnancy and other conditions typically presenting in the first trimester are not considered in this brief review.

Several difficulties arise when surgical intervention is contemplated in pregnancy:

1. All interventions carry a risk to the fetus. Premature labour and the risk of miscarriage or delivery of an immature fetus are primary concerns.
2. The physiology of pregnancy has an impact on symptoms, signs and the interpretation of routinely performed tests in patients with abdominal pain.
3. Imaging studies, particularly where radiation is used, have been regarded as posing unsupportable risks to the fetus.
4. The use of medications has to have due regard to the risk of fetal injury.

A cumulative literature has placed restrictions on the timing of surgical interventions in pregnancy to reduce the incidence of premature labour. In general terms, expeditious treatment of the mother always benefits the fetus. There are few exceptions to this rule, but grave ethical issues, with legal implications that will try the resources of individuals and institutions, arise rarely.

Over the last decade or so, there has been a gradual review of the accumulated wisdom of the previous half century. This relates mainly to the timing of surgical interventions in the different trimesters of pregnancy, the use of x rays as an adjunct to diagnosis and the place of laparoscopy. Further, accurate peri-operative monitoring of mother and fetus is now widely available and allows timely correction of abnormalities, particularly the prevention of premature labour with the use of tocolytics.

Physiological changes

As the uterus enlarges it occupies the pelvis and becomes an abdominal organ by 14 weeks, pushing the caecum upward and laterally, but the appendix tends to rotate medial and away from the abdominal wall. The latter begins to stretch and the usually reliable sign of guarding and rigidity may be attenuated, though localised tenderness over the area of an inflamed viscus will remain.

Progesterone causes hypotonia and visceral dilatation, affecting the function of the stomach, colon and gall-bladder. Gastric emptying is delayed and gastro-oesophageal reflux increased; constipation is a frequent accompaniment. The ureters dilate, which is worsened by the direct weight of the enlarging uterus and fetal head. Asymptomatic bacteriuria and pyuria occur in up to five per cent of normal pregnancies and may herald pyelonepritis if not vigorously treated. The bile becomes more lithogenic and the incidence of gall stones increases with pregnancy and parity.^1-3

The circulation becomes hyperdynamic, with resting tachycardia, widened pulse pressure, raised blood volume and increased cardiac output. As the uterus enlarges, diaphragmatic function is impeded and functional residual capacity and vital capacity decrease. Mucosal immunity may be decreased. Pregnancy is considered a thrombogenic state, with a predisposition to deep vein thrombosis and pulmonary embolus.

Imaging in pregnancy

Ultrasound (US) is the baseline investigation in most pregnant patients with abdominal pain.⁴ It is generally available at short notice in most hospitals and there is no evidence of it causing harmful effects to the fetus. It has good levels of sensitivity and specificity in the diagnosis of many causes of abdominal pain, in both the realm of gynaecologist and surgeon. However, US is operator dependent and it is sometimes useful for the surgeon to be present at the examination to assess the response of the patient to pressure by the US probe over an area of US-demonstrated abnormality. This information alone may be sufficient to make or exclude a diagnosis.

Ionising radiation

Uppermost in the minds of pregnant women that are recommended diagnostic radiology are the risks of:

1. Early abortion and miscarriage, with a background frequency of this occurring of between three and 15 per cent;
2. Physical and intellectual developmental delay, with a background frequency of between one and three per cent; and
3. Childhood cancer, with a background frequency of this occurring of between 0.2 and 0.3 per cent.

There seems little doubt that significant radiation exposure can contribute to any of these adverse outcomes, and both radiation dose and gestational age are relevant. The risk of fetal loss is highest in the first two weeks after conception, the teratogenic and intellectual developmental delay risks are maximal between weeks eight and 17, and radiation in the third trimester may increase the risks of childhood malignancy.^5-7 However, in the usual doses associated with medical imaging, these risks are considered to be extremely low.

Much of the medical literature on radiation dose refers to rads or milirads. The rad represents the absorbed dose of energy in Joules /Kg, 1 Gray (Gy) is equivalent to 100 rad. The biological effect of this energy is derived by multiplying absorbed dose (rads or Gy) by a quality factor varying with different tissues to give an overall value, the ‘effective dose’, measured in Sieverts, Sv. One Sv is equal to 1000 mSv in the usual way, and 1 mSv is equal to 100 mrem. I will confine my remarks to these units (there are several others, unfortunately). Useful resources for patients may be found at the websites of the Health Physics Society and the American College of Radiology.

The annual dose of background radiation is usually given as 300 mrem, 3 mSv, but can vary with place and altitude. A single chest x ray delivers 10 mrem, 0.1 mSv, three per cent of the background annual dose. An abdomino-pelvic CT scan may deliver 15 mSv, (and sometimes considerably more, depending on equipment and technique), which amounts to five years’ worth of background radiation. This will increase the above risks to the fetus of about one extra case in 6000 exposures, which is considered acceptable.

The onus then is very much on the attending clinician’s judgement on the requirement for an abdomino-pelvic CT scan. If there are important threats to the mother and a CT will facilitate and expedite treatment, it should be recommended after appropriate discussion with the mother. Neither should this be a routine request to the radiology department; there should be detailed discussion between clinician and radiologist regarding the minimisation of the radiation risk, the use of contrast and positioning.

Most guidelines suggest a radiation dose of 5 rad at any one study in pregnancy is acceptable (in other words, approximately one abdomino-pelvic CT scan), and a maximum of 20 rads during the course of a pregnancy, in exceptional circumstances. Beyond this level the accumulated radiation doses become ‘significant’ and the hazard to the fetus unacceptable.^5-7

Fluoroscopy

The estimated radiation dose of fluoroscopy is approximately 20 rad per minute. The common indications for fluoroscopy in this setting will be operative or endoscopic cholangiography. The fetus can be appropriately shielded during these interventions to reduce this further. Most such procedures can be completed with an exposure of 1 rad.

Magnetic resonance imaging

High-quality images are possible with this modality, which does not use or produce ionising radiation. Recent reports have shown that magnetic resonance imaging (MRI) can diagnose many sources of abdominal pain in pregnancy with high sensitivity and specificity. MRI has not been shown, so far, to have any effects on the fetus and the American College of Radiologists has recommended that this modality can be used in all stages of pregnancy in informed patients, but experience is limited. In selected cases, MRI can be offered to pregnant patients after appropriate counselling and documentation. Not enough is known about the MRI contrast agent Gadolinium and its effects on the fetus, and it cannot be recommended.⁹ Pregnant patients may have difficulty lying still for the time required for image acquisition, up to 20 minutes, and of course it is not suitable for unstable patients.

Laparoscopy in pregnancy

The explosion of laparoscopic applications in general surgery began in the early 1990s, but was not immediately mirrored in the management of pregnant patients. There were several reasons for this:

1. the risk of uterine injury during the induction of pneumoperitoneum;
2. the possibility of fetal acidosis;
3. the cardiovascular effects of pneumoperitoneum; and
4. concern about the gravid uterus impairing vision, particularly for lower abdominal procedures.

Several series of successful laparoscopy have now been reported, including complex laparoscopy in all trimesters of pregnancy, with all the benefits associated with the technique in non-pregnant patients. What has also become evident is that the proscriptions of surgery in the first and third trimesters may not apply to laparoscopy and may represent the atraumatic nature of well-performed keyhole surgery, minimising direct pressure on the gravid uterus. Neither has there been reported an increased incidence of adverse events in later childhood.

Series using Verres needle induction as well as open induction have been reported with no uterine injury. It does seem that the operator may apply his or her usual technique, having regard to the position of the uterus and the attenuation of the abdominal wall. The supine position in advanced pregnancy is tolerated poorly. Compression of the inferior vena cava (IVC) by the gravid uterus may be exacerbated by pneumoperitoneum, diminishing venous return, cardiac output and blood pressure. The patient should be tilted 15 degrees to the left to decrease pressure on the IVC, which allows induction and maintenance of pneumoperitoneum.

The relationship between maternal arterial pCO₂ and acidosis in the fetus during laparoscopy has been established in experimental animals. While a similar relationship is probable in humans, it does not appear to be a significant issue in clinical practice. End tidal CO₂ measured at intra-operative capnography is considered sufficient indication of arterial pCO₂ and continuous measurement of maternal arterial CO₂ is not thought necessary. Nonetheless, laparoscopy should be completed expeditiously by expert surgeons, supported by trained anaesthetists with full access to monitoring the anaesthetised pregnant patient.^{5, 8, 10}

Threatened labour in the postoperative pregnant patient with a viable fetus is an indication for monitoring and the use of tocolytics. There is no evidence to support prophylactic use of tocolytics in this setting.

Clinical scenarios

Right lower quadrant abdominal pain and tenderness¹¹

A considerable differential diagnosis is present (see Figure 1). Appendicitis can occur at all stages of pregnancy. It is the commonest cause for non-obstetric surgery and the diagnosis should be vigorously pursued. In uncomplicated appendicitis the rate of fetal wastage is up to two per cent, but increases to 30 per cent with perforation and peritonitis, with a real risk of maternal mortality. Fully a quarter of pregnant patients will have perforation at surgery. Most surgeons would arrange for US in the work-up, but exploratory surgery with a high index of suspicion, particularly if performed laparoscopically can be considered a diagnostic and therapeutic intervention. A negative appendicectomy rate of 25 per cent is considered acceptable.

Table 1. Differential diagnosis of appendicitis in pregnancy

Many pregnant patients with appendicitis will have an abnormal urine and this should not reassure the surgeon. Other evidence should be sought, otherwise it is better to ‘look and see’ rather than ‘wait and see’.

Differential diagnosis of RUQ pain and tenderness

Gall bladder pain and cholecystitis are common accompaniments of pregnancy. Expertly performed acute cholecystectomy with or without cholangiography as indicated is the appropriate treatment in all trimesters, conferring benefits on pregnant and non-pregnant patients alike.^{8, 10} Common sense suggests that the first month and the last month of pregnancy are best avoided. Two-thirds of patients continue to have symptoms of recurrent pain and cholecystitis with attendant morbidity, in addition to the risks of jaundice and pancreatitis occurring in patients managed expectantly. Not all patients with gall stones and RUQ pain will have symptomatic cholelithiasis. The US examination may provide clear evidence of this, but other pathology in the RUQ should be sought by the sonographer, particularly in the liver. Solid lesions in the liver, particularly those larger than 5 cm, may be a cause of pain and have important implications. Hepatic adenomas are associated with oral contraceptive use and their incidence is probably increasing. Their behaviour in pregnancy may be unpredictable and should be monitored with serial US, with the input of a liver surgeon.1 The diagnosis of liver lesions may require CT with contrast and MRI, in order that prognosis be assessed. Radiation to the fetus can be minimised using a lead apron over the lower abdomen.

While reflux oesophagitis is common in pregnancy, gastric and duodenal ulcer is uncommon. Endoscopy is acceptable at all stages of pregnancy. The mainstay of treatment for reflux is antacids in addition to dietary and positional advice. Histamine receptor antagonists, ranitidine being the safest, may be required. Proton pump inhibitors (PPI) are best left in reserve for the most severe cases, though a recent meta-analysis of PPI use in pregnancy has been reassuring.¹²

Pancreatitis should be managed in the usual manner. Common bile duct stones should be sought, particularly in severe pancreatitis, and treated with expeditious endoscopic retrograde cholangiopancreatography (ERCP) and sphincterotomy. Pregnancy does not provide any protection from the high mortality rates associated with severe pancreatitis of up to ten per cent. Gallstone pancreatitis should be treated with cholecystectomy when the pancreatitis has settled and not deferred.¹³

Table 2. Differential diagnosis of RUQ pain and tenderness

After appendicitis and cholelithiasis, intestinal obstruction is the third most common cause for non-obstetric surgery in pregnancy. The commonest cause is small bowel obstruction (SBO) secondary to abdominal adhesions, and this is increasing in frequency.

SBO is maximal in the third trimester and puerperium as visceral relationships may suddenly change. The classical symptoms of abdominal pain, distension, vomiting and constipation may not be as obvious as in the non-pregnant and when the quality of the pain changes from moderate and colicky to continuous and severe, strangulation may be imminent. Localised tenderness may also point to operative intervention. A plain abdominal x ray may well make the diagnosis. If further prognostic information is required, gastrografin follow through, and abdominal CT scan may select those patients in whom resolution is unlikely. This combination of imaging could still be achieved within the 5 rad limit and if it enhances the rapidity of the diagnosis should be performed. The management of adhesional SBO is no different from that in the non-pregnant patient. Intravenous fluids, naso-gastric suction, analgesia and prompt surgery where indicated will provide best outcomes for mother and fetus.

Abdominal catastrophes in pregnancy

Major bleeding in pregnancy is part of the grim routine of obstetricians; surgeons, fortunately, rarely need to get involved. Shock is often compounded by coagulopathy and careful and vigorous transfusion of blood products will be required as the patient is prepared for the operating theatre or delivery room. Haemorrhage from within the uterus may be associated with abruptio placentae and present with vaginal bleeding, abdominal pain and tenderness. This may occur in the setting of the patient with preeclampsia and fetal distress, and the decision may be taken for early caesarean section.

Table 3. Abdominal catastrophes in pregnancy

In preeclamptic patients with major extra-uterine haemorrhage, the usual source is bleeding into the liver as part of the HELLP syndrome (H-haemolysis, EL-elevated liver enzymes, LP-low platelets), associated with considerable mortality rates for mother (one to two per cent) and fetus (up to 30 per cent). The priority is to deliver the fetus, which over a period of two or three days should allow the intravascular pathology associated with the syndrome to resolve. Subcapsular haematoma occurs in between one and two per cent of patients with HELLP syndrome and angiography and embolisation may allow control of continuing bleeding. Major rupture of the liver capsule may need laparotomy and skilled packing. Rarely, formal liver resection may be required to save life.

Major bleeding may also arise elsewhere in the abdomen. The patient should be rapidly resuscitated using the usual advanced trauma life support (ATLS) principles and limited imaging may be possible to help make a diagnosis. This may be a US scan to confirm intra-abdominal bleeding, but a CT scan if possible may be quite helpful to direct the surgeon. An assessment of the fetal heart can be made and if absent may not need to be repeated. The mother takes priority and whatever surgery is required should be performed promptly. Such surgery may involve splenectomy and aneurysmectomy for rupture of a splenic aneurysm, or spontaneous splenic rupture, or to pack or resect a lesion in the liver.^{3, 5} The fetus tolerates maternal hypotension poorly and a caesarean section may be appropriate, particularly if it is needed to improve access to the bleeding lesion in the abdomen. This may also enhance the vascular dynamics of venous return and cardiac output.

A brief word on trauma in pregnancy

Close to 50 per cent of all maternal deaths are related to trauma, arising from motor vehicle accidents, falls and assault. Trauma is the cause of up to five per cent of fetal mortality. The ATLS pattern is quickly initiated with a few important variations. An obstetrician is involved in the secondary survey to assess the gestational age and the condition of the fetus and the pregnancy. An US is part of this process and will demonstrate free intraperitoneal bleeding, if present, and may show an abruption, though clinical and vaginal examination may have already suggested this. Most abruptions will declare themselves in the first four hours post-trauma and fetal monitoring will be needed for this period. Ongoing monitoring will be a decision for the obstetrician. In advanced pregnancy blood volume and cardiac output may increase substantially and the first signs of major bleeding may be fetal distress. Whatever imaging is required and possible should be performed including abdomino-pelvic CT scans. The constraints above regarding radiation doses should be kept in mind and attempts to use shielding should be made where possible. If there are absolute indications for urgent laparotomy this should proceed. Strong indications for caesarean section may then exist, particularly if ongoing instability is expected, and will be issues that will exercise the minds of all clinicians involved.¹⁴