Abstract
Key Implications
Key Facts
Acute abdomen refers to abdominal pain of less than 1 week’s duration requiring admission to hospital, which has not been previously treated or investigated.
Abdominal pain in pregnancy may be secondary to the anatomical and physiological changes of the pregnant state or may be totally unrelated to pregnancy.
Abdominal pain of any degree is a cause of significant maternal anxiety and constitutes a major reason for hospital attendance during pregnancy.
The gravid uterus enlarges to almost 20 times its normal ‘non-pregnant’ size, which results in stretching of the supporting ligaments and muscles as well as pressure on the other intra-abdominal structures and layers of the anterior abdominal wall.
20% of adnexal torsions occur during pregnancy – this rarely includes torsion of a morphologically normal ovary.
Key Implications
Physiological leukocytosis and raised alkaline phosphatase levels that are associated with normal pregnancy may contribute to diagnostic difficulty.
Imaging techniques such as radiography, magnetic resonance imaging (MRI) or computerised tomography (CT) to diagnose non-obstetric causes of abdominal pain may be delayed, due to the fear of exposing the fetus to radiation.
Although there is a risk of teratogenesis in the first trimester and possible link to childhood cancers with late fetal exposure to ionising radiation, exposures of less than 0.05 Gy have not been associated with pregnancy loss or fetal malformations [1].
CT should not be the initial imaging modality in pregnancy, except when urgent information is required [2–4].
Radiation exposure to the fetus can be up to 50 mGy with a CT scan of the abdomen and pelvis.
This can cause teratogenesis and increases the risk of developing childhood malignancies such as leukemia [5–9].
MRI, although not readily available, provides similar or better accuracy in diagnosing non-trauma-related intra-abdominal pathology as compared to CT or ultrasound [10, 11].
Due to anatomical changes associated with pregnancy, classic symptoms and signs that are observed in the non-pregnant state may be distorted. For example, certain organs such as the appendix are progressively displaced upwards and laterally with advancing gestation by the enlarging gravid uterus. Hence, the point of maximum tenderness may not be felt around the McBurney point.
Further, the visceral innervation of the reproductive organs is the same as that of the recto-sigmoid and terminal ileum [12].
Key Pointers
Miscarriage
A combination of pain and vaginal bleeding should alert a clinician to a possible threatened, inevitable, incomplete or septic miscarriage. Pain is typically described as a ‘cramping ache’. On examination, the fundal height of the uterus corresponds to the period of amenorrhoea and signs of peritoneal irritation are absent. The internal cervical os might be open or closed based on the type of miscarriage. An open os is diagnostic of an inevitable or incomplete miscarriage. Ultrasound examination is helpful to confirm viability, intra-uterine pregnancy and exclude a subchorionic haematoma [13].
Ectopic Pregnancy
Pregnancy is rarely located outside the normal endometrial cavity, most commonly in the Fallopian tubes. Pain is typically unilateral and colicky. It may be superimposed on ‘dull aching pain’ and may be associated with dizziness or fainting episodes. On clinical examination, unilateral iliac fossa tenderness, cervical excitation and adnexal tenderness may be elicited. The size (i.e. the measured fundal height) of the uterus is often less than what would be expected for the period of amenorrhoea.
Demonstration of an empty uterine cavity on transvaginal ultrasound despite serum beta HCG levels of over 1500 IU/L may help clinch the diagnosis.
Presence of any symptoms including abdominal pain or evidence of significant haemoperitoneum is a contraindication for medical treatment and surgical treatment is indicated. This includes emergency salpingectomy via laparoscopy or laparotomy.
Ovarian Cyst ‘Accidents’
Ovarian cysts complicate 1 in 1000 pregnancies and a vast majority are benign (98%). Pain is often described as intermittent and unilateral. Torsion also occurs more frequently on the right than the left, by a ratio of 3:2, owing to the presence of the sigmoid colon on the left that limits the space available for torsion. Clinical examination may confirm tenderness in either iliac fossa and a large cyst may be palpable during abdominal and/or bimanual examination. However, in modern obstetric practice, the cyst is usually detected on ultrasound. Figure 24.1 shows a dermoid cyst complicating pregnancy.
Figure 24.1 Ovarian (dermoid) cyst complicating pregnancy.
Most torsions and cyst accidents present as an acute abdomen and would warrant surgical treatment. Twenty per cent of adnexal torsions occur during pregnancy –this also includes torsion of a morphologically normal ovary. About 50% of cases of adnexal torsion have an associated ovarian mass [14].
In early pregnancy, symptomatic ‘benign’ ovarian cysts may be removed by laparoscopic ovarian cystectomy. In view of the inaccessibility of the adnexae in late pregnancy, a midline or paramedian incision is recommended. Any ovarian cyst that exhibits sonographic features that are suggestive of malignancy should be referred to the oncological team for further imaging and appropriate treatment.
Acute Retention of Urine
Pain due to retention of urine caused by stretching of, or direct pressure on, the urethra may be due to a retroverted uterus in early pregnancy or rarely due to an impacted pelvic mass such as an ovarian cyst or a fibroid mass. An indwelling catheter to facilitate bladder drainage may help relieve pain. Gentle manual correction of the retroversion and an indwelling catheter should be the conservative management plan until the uterus rises above the pelvis at 12 weeks’ gestation.
Musculoskeletal Causes
Round ligament pain is a common cause of antenatal attendance in the second and third trimesters. This often presents with pain in one or both iliac fossae. It is believed to be secondary to the stretching of the ligamentous supports of the uterus. The pain is characteristically worse on movement. A support brace and simple analgesia are the mainstays of treatment.
Ovarian Hyperstimulation Syndrome
This is a systemic condition secondary to the production of vasoactive substances produced by hyperstimulated ovaries. The diagnosis is very straightforward, as there is a history of undergoing assisted conception with ovulation induction. Associated symptoms are a result of increased capillary permeability and include headache, vomiting, abdominal distension and rarely oliguria. Based on clinical severity, the initial classification of Schenker and Weinstein [15] has been modified by Golan et al. into six grades [16].
Ovarian hyperstimulation syndrome is a potentially life-threatening condition and immediate senior input should be sought and a multidisciplinary care plan should be instituted. Management includes supportive treatment for pain and correction of intravascular dehydration, replacement of albumin, daily weight chart and thromboprophylaxis. Some women may require an urgent laparotomy (multiple cyst rupture) and treatment in an intensive treatment unit.
Gastritis and Hyperemesis Gravidarum
Gastritis typically occurs up to 16 weeks’ gestation and resolves by treatment with fluid replacement, antiemetics and H2 blockers. Persistent vomiting may rarely lead to Mallory–Weiss tears in the lower oesophagus and resultant haematemesis and abdominal pain. Urgent referral to the upper gastrointestinal surgical team for tamponade using a Sengstaken–Blakemore tube should be made if this condition is suspected.
Fibroid Degeneration
Fibroids occur in 1% of all pregnancies and risk of torsion is increased in the pedunculated variety. Red degeneration presents with severe, localised pain and is associated with nausea and vomiting. Ultrasound examination may reveal cystic spaces within the fibroid suggestive of degenerative changes. Conservative management with opiate analgesia and reassurance is required.
Ruptured Rudimentary Horn
This is extremely rare with a quoted incidence of 1:76 000 and presents with persistent severe uterine pain refractory to simple analgesia. This mullerian tract abnormality typically ruptures in the second trimester and is associated with significant intraperitoneal bleeding. Rarely, it may rupture into the broad ligament (Figure 24.2).
Figure 24.2 Rupture of a pregnancy within the uterine horn at 22 weeks.
Obstetric Complications
Placental Abruption
Abruptio placenta refers to the premature separation of a normally situated placenta and it occurs in 0.5%–1.5% of all pregnancies.
Abdominal pain may present with or without vaginal bleeding. Fetal heart rate may be absent in severe abruption secondary to utero-placental insufficiency.
There may be varying degrees of haemodynamic compromise secondary to blood loss either vaginally or inside the uterus in the concealed variety [17].
Immediate senior input should be sought and management includes maternal resuscitation, correction of hypovolaemia and coagulation abnormalities through a multidisciplinary approach. Emergency caesarean section should be performed in the event of suspected fetal compromise, once the woman is haemodynamically stable and her coagulation abnormality is corrected.
If an intrauterine death is confirmed, an amniotomy and oxytocin infusion may be commenced. Haemodynamic instability warrants immediate uterine evacuation to avoid morbidity and maternal mortality.
Acute polyhydramnios
Acute polyhydramnios refers to an amniotic fluid index above the 95th centile for gestational age or the depth of the deepest vertical pool equal to or greater than 8 cm.
Abdominal pain in acute polyhydramnios is secondary to uterine over-distension. Clinical signs include an elevated symphyseal fundal height, difficulty in palpating fetal parts due to a tense and tender abdomen. On examination, a fluid thrill may be elicited on percussion. Confirmatory diagnosis is by ultrasound measurement of amniotic fluid pockets.
Management should involve specialists in fetal medicine and may include immediate amnio-drainage to relieve symptoms and to reduce the risk of preterm labour. Laser ablation of vascular anastomosis (twin-to-twin transfusion syndrome), serial amnioreduction to relieve pressure on the placental bed may be considered at a later stage. Predisposing causes such as congenital malformations and undiagnosed diabetes mellitus should be excluded. Indomethacin may help reduce formation of amniotic fluid but may adversely affect fetal renal function and therefore it is not recommended for prolonged use.
Uterine Scar Dehiscence
The incidence of intrapartum scar dehiscence is 35:10 000 after one caesarean section. Spontaneous rupture of a non-scarred uterus may occur in grand multiparous women with obstructed labour and excessive use of oxytocin or prostaglandins.
Women may present with acute pain between uterine contractions, vaginal bleeding and signs of circulatory collapse. Rarely, if the fetus has been extruded into the peritoneal cavity, fetal parts and uterine asymmetry might be obvious.
The earliest sign of intrapartum scar dehiscence is fetal compromise on the cardiotocograph (CTG). Management involves maternal resuscitation and immediate laparotomy, delivery of the fetus, placenta and repair of the dehisced uterus.
Acute Chorioamnionitis
Pre-labour rupture of membranes typically precedes chorioamnionitis. However, infection may be present with intact membranes and leads to severe abdominal pain.
Pain is usually associated with maternal and fetal tachycardia, pyrexia and offensive vaginal discharge. In extreme cases there may be widespread septicaemia/ systemic inflammatory response syndrome (SIRS) and features of septic shock. The recent CMACE report has flagged genital tract sepsis as a leading cause of direct maternal death in the last triennium [18].
Recognising Symptoms and Signs of Sepsis
Reduced mental alertness, sometimes with confusion
Nausea and vomiting
Diarrhoea
Increased heart rate, greater than 90 beats/minute
Increased respiratory rate, greater than 30 breaths/minute
High or low white blood cell count; low blood pressure
Altered kidney or liver function
Aggressive treatment with intravenous, broad-spectrum antibiotics within 1 hour of diagnosis, fluid resuscitation and expediting delivery to remove the focus of infection are essential [19]. Management in accordance with the ‘Surviving Sepsis Campaign’ [20] should be implemented. This includes fluid resuscitation, immediate intravenous broad-spectrum antibiotics and correction of metabolic acidosis initially, followed by inotropes, vasopressors, corticosteroids and mechanical ventilation, if required.
Uterine Torsion
The uterus rotates axially by 30° to the right in approximately 80% of all pregnancies. Torsion may occur when this rotation extends beyond 90°, causing severe abdominal pain, uterine tenderness and urinary retention in the last trimester of pregnancy. Predisposing factors include fibroids, ovarian cysts, mullerian tract abnormalities and pelvic adhesions. A displaced urethra at catheterisation may lead to the diagnosis. Conservative treatment includes analgesia and change in maternal position with caesarean section being reserved for severe cases [21].
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