Introduction

Abdominal pain in pregnancy may be difficult to diagnose. Urgent hospital referral is often required, unless a benign cause can be established with certainty in the absence of maternal or fetal distress.

Assessment of abdominal pain is more complex in pregnant women because uterine enlargement may hide classical signs. Peritoneal signs may be absent due to lifting of the abdominal wall. Abdominal organs can change position as the pregnancy progresses - for example, the appendix is displaced upwards and laterally towards the gallbladder after the first trimester.^[1]

The assessment must consider both maternal and fetal wellbeing, bearing in mind intra-abdominal infection or inflammation can be associated with premature labour or fetal loss,^[1] and that acute conditions such as appendicitis carry higher risks in pregnancy.^[2] Patients may need joint assessment by both gynaecological/obstetric and surgical teams. Where the diagnosis is unclear, the risks of exploratory surgery must be balanced against the risks of delayed diagnosis.^[3]

Aetiology^[1][2][3][5]

Acute appendicitis is the most common cause of an acute abdomen during pregnancy. Urinary tract infection (UTI) or stones and cholecystitis are also relatively common.

The following section lists the more likely causes of abdominal pain during pregnancy. For a more extensive list of non-pregnancy-related causes, see separate Abdominal Pain article.

Obstetric causes^[6][7]

• Labour pain - premature labour or term.
• Pre-eclampsia or HELLP syndrome - epigastric or right upper quadrant pain.
• Placental abruption:^[6]
  • Typically, sudden severe pain and a 'woody' hard, tender uterus; fetal distress, ± vaginal bleeding.
  • With posterior placenta, pain and shock may be less severe, with pain felt in the back; diagnose by pattern of fetal contractions (excessive and frequent) with fetal heart pattern suggesting hypoxia.
• Uterine rupture:
  • Constant pain, profound shock, fetal distress and vaginal bleeding; usually presents during labour and with history of uterine scar.
  • Rarely, occurs without labour and without uterine scar.
• Chorioamnionitis:
  • This usually follows premature rupture of membranes, but can occur with membranes intact.
• Acute fatty liver of pregnancy:
  • Presents in the second half of pregnancy with abdominal pain, nausea/vomiting, jaundice, malaise and headache.
• Acute polyhydramnios
• Rupture of utero-ovarian vessels.^[8]
• Severe uterine torsion^[9]- rare; may be due to structural abnormalities in the pelvis.
  • Presents in the second half of pregnancy with variable symptoms, including severe abdominal pain, tense uterus, retention of urine ± shock and fetal distress; or, it may be asymptomatic; the fetus is at risk.

Gynaecological causes

• Ectopic pregnancy:^[10] 
  • Usually presents between 5-9 weeks' gestation.
  • The classical triad of bleeding, abdominal pain, and amenorrhoea is not present in many women; symptoms and signs are often nonspecific; the diagnosis can only be confirmed in secondary care.
  • Symptoms vary and include: syncope, dysuria (including dipstick urine findings suggesting UTI), diarrhoea and vomiting, subtle changes in vital signs; adnexal tenderness may be absent; a history of 'missed period' may be absent if vaginal bleeding is mistaken for a normal period.
• Miscarriage ± septic abortion.
• Torsion of the ovary or Fallopian tube.^[11]
• Ovarian cysts - torsion, haemorrhage or rupture.
• Fibroids - red degeneration or torsion.^[12]
• Ovarian hyperstimulation syndrome:^[13]
  • A complication of gonadotrophin-assisted conception; can occur pre-conception or in early pregnancy.
  • Large ovarian cysts cause abdominal pain and distention and, in severe cases, also fluid shifts, ascites, pleural effusion and shock.
• Salpingitis.
• Round ligament pain.

'Surgical' causes

• Acute appendicitis.^[14]
  • Presents with fever, anorexia, nausea, vomiting, right iliac fossa (RIF) pain.
  • After the first trimester, the pain may shift upwards towards the right upper quadrant, but does not always do so - and patients in all trimesters may have RIF pain.
  • With retrocaecal appendix, may have back or flank pain.
• Cholecystitis and gallstones.
• Urinary tract - renal calculi, urinary tract obstruction (including acute urinary retention due to retroverted gravid uterus).
• Intestinal obstruction - most often due to adhesions.
• Peritonitis from any cause.
• Abdominal trauma, including domestic violence.^[15]
• Mesenteric adenitis.
• Meckel's diverticulitis.
• Peptic ulcer.
• Inflammatory bowel disease.
• Abdominal wall - hernias, musculoskeletal pain, rupture of rectus abdominis muscle.
• Acute pancreatitis - rare and usually due to gallstones.
• Mesenteric venous thrombosis (rare) - most reported cases have occurred where dehydration complicated an underlying hypercoagulable state.^[1]
• Rupture of visceral artery aneurysm (rare).

'Medical' causes

• UTI ± pyelonephritis.
• Constipation.
• Diabetic ketoacidosis.
• Sickle-cell anaemia crisis.
• Lower lobe pneumonia.
• Venous thromboembolism - deep vein thrombosis or pulmonary embolus may cause lower or upper abdominal pain respectively.^[16]
• Myocardial infarction.
• Gastroenteritis.
• Irritable bowel syndrome.

Musculoskeletal causes

• Round ligament pain - low abdominal or groin pain due to the uterus pulling on the round ligament.
• General aches - due to uterine enlargement.
• Rectus muscle haematoma - due to rupture of inferior epigastric vessels in late pregnancy:
  • Presents with sudden severe abdominal pain, often after coughing or trauma.
• Pelvic girdle pain:
  • Symphysis pubis dehiscence.
  • Osteomalacia may present in pregnancy due to increasing vitamin D requirements.

Assessment

History

• Pain history - nature, location and radiation, onset, exacerbating or relieving factors. These will give clues about the cause (see separate article on Abdominal Pain for details).
• Other abdominal symptoms - vaginal bleeding, bowel and urinary symptoms; pre-eclampsia symptoms (eg headache, visual change, nausea).
• Fetal movements.
• Obstetric history - last menstrual period (LMP); confirm whether the patient's last bleed was 'normal' for the patient (ectopic pregnancy may have some bleeding which can be mistaken for menstrual bleed); ascertain if there has been any difficult or assisted conception; confirm use of any contraception (coil and progestogen-only pill (POP) increase ectopic risk).
• Past medical and gynaecological history, medication, allergies, last meal.

Examination^[1][3]

• General examination - well/ill, signs of sepsis, shock or haemorrhage, blood pressure, urine dipstick protein and glucose.
• Assess the pregnancy and uterus:
  • Palpate uterus for fundal height, contractions or hard uterus, polyhydramnios, fetal position and presentation.
  • Assess fetal wellbeing - movements or heartbeat (auscultate, Doppler scan or cardiotocography (CTG)).
• Abdominal examination - see separate Abdominal Examinationarticle, but note the differences in pregnant patients:
  • To distinguish extra-uterine from uterine tenderness, lie the patient on her side, thus displacing the uterus.
  • Clinical signs may be less distinct.
  • Peritoneal signs may be absent in pregnancy, as the uterus can lift the abdominal wall away from the area of inflammation.
  • Note the changing positions of the intra-abdominal contents as the pregnancy progresses. The appendix is located at McBurney's point in patients in the first trimester, but then moves upward and laterally towards the gallbladder. The bowel can be displaced into the upper abdomen.
• Consider whether vaginal and/or rectal examination is indicated:
  • Never do vaginal examination if placenta praevia is suspected (vaginal bleeding in the second half of a pregnancy) - it could cause a massive bleed.
  • Suspected rupture of membranes requires sterile examination and should be done in an obstetric unit.
  • For incomplete miscarriage with heavy bleeding, examine the cervical os. Products in the os may cause heavy bleeding, and also bradycardia/shock due to vagal stimulation. Remove products in the os (using sponge forceps) to reduce bleeding and pain.^[4]

Investigations

Bedside tests

• Urine dipstick
• Urine pregnancy test
  • Urine beta human chorionic gonadotrophin (beta-hCG) tests are sensitive, detecting beta-hCG at 25 IU/L (a level normally reached 9 days post-conception).^[17] A negative urine beta-hCG result does not absolutely rule out an ectopic pregnancy - if discordant with the clinical picture, arrange serum beta-hCG or an urgent assessment.
• Bedside glucose test.
• Fetal CTG monitoring.

Initial investigations

• Blood tests - depending on the clinical scenario, consider:
  • FBC.
  • Group and save/cross-match.
  • Rhesus blood group (if not known).
  • Serum beta-hCG - can aid diagnosis/management decisions regarding suspected ectopic pregnancy or miscarriage.^[17][18]
  • Biochemistry: renal and liver function, glucose, calcium, amylase, hepatitis serology.
  • Clotting screen if haemorrhage, placental abruption or liver disease suspected.
  • Sickle cell screen.
  • Blood film (for evidence of haemolysis, if HELLP syndrome is suspected).
• Urine tests:
  • Urine microscopy and culture.
  • Urine protein quantification for suspected pre-eclampsia.
• ECG if atypical epigastric pain.
• Ultrasound:
  • First trimester - can confirm whether pregnancy is intra-uterine and viable. From 5+ weeks a sac is visible and from 6 weeks the fetal heartbeat is seen. Free fluid in the pelvis suggests ectopic pregnancy.^[18] Transvaginal ultrasound is more sensitive in early pregnancy.
  • Second-third trimesters - gives information about fetal wellbeing, the uterus and placenta.
  • May assist surgical diagnosis, eg acute appendicitis, ovarian cysts, gallstones.^[2]

Further investigations

• Chest X-ray, if required, involves negligible radiation dose to the fetus.^[16]
• Swabs and/or blood cultures if there is suspected infection/sepsis.
• MRI (if feasible) can be used to evaluate pregnant patients with acute lower abdominal pain where an extra-uterine cause is suspected.^[19]
• CT scans have been used in the second and third trimesters, but involve significant radiation.^[14]
• Diagnostic laparoscopy or laparotomy may be required. Laparoscopy is feasible and useful in pregnancy.^[2]

Further management^[1]

This depends on the diagnosis, but some general points are:

• Rhesus-negative women - give anti-D immunoglobulin if indicated.
• Combined management by an obstetrician, surgeon and/or physician may be needed.
• Indications for emergency surgery are similar to non-pregnant patients.
• If non-urgent surgery is required during pregnancy, the second trimester is preferred.
• Laparoscopy is increasingly used for diagnosis and treatment.