Acute Abdominal Pain in Pregnancy
Differential Diagnosis
Common Diagnoses
- Symphysis Pubis and Ligament Strain
- Miscarriage: 20%–40% of Pregnancies in First Trimester
- Labour: 6% Premature
- Placental Abruption
- Pyelonephritis (Especially Around 20 Weeks)
Occasional Diagnoses
- Constipation (Common Cause but Only Occasionally Presents)
- Ectopic Pregnancy (1/250 Pregnancies)
- Appendicitis (1/1000 Pregnancies)
- Red Degeneration of Fibroid
- Torsion/Rupture of Ovarian Cyst or Tumour
Rare Diagnoses
- Uterine Rupture (in UK 1/1500 Pregnancies, of Which 70% Due to Caesarian Scar Dehiscence)
- Uterine torsion (Axial Rotation >90°): 90% Associated with Fibroids, Adnexal Masses and Anatomical Uterine Anomalies
- Liver Congestion Due to Pre-Eclampsia
- Rectus Sheath Haematoma
Ready Reckoner
Key distinguishing features of the most common diagnoses
| S. Pubis Strain | Miscarriage | Labour | Abruption | Pyelonephritis | |
|---|---|---|---|---|---|
| Localised Tenderness | Yes | No | No | Possible | Yes |
| Crampy Pain | No | Yes | Yes | No | No |
| Vaginal Bleeding | No | Yes | No | Yes | No |
| Uterine Rigidity | No | No | No | Yes | No |
| Fever, Unilateral Pain | No | No | No | No | Yes |
Possible Investigations
Likely:Urinalysis, MSU.
Possible:Ultrasound, FBC.
Small Print:Laparoscopy.
- Urinalysis: Proteinuria in pre-eclampsia. Blood, pus cells and nitrite in urinary tract infection (UTI); the infecting organism will be confirmed on MSU.
- FBC: Raised WCC in UTI.
- Imaging ultrasound can be diagnostic in abruption and miscarriage; the presence of an intrauterine pregnancy makes an ectopic very unlikely; ultrasound may also be helpful in detecting a rectus sheath haematoma.
- Laparoscopy: To confirm ectopic pregnancy.
Top Tips
- Pain on standing and walking, and relieved by rest, with exquisite pubic symphysis tenderness, is ‘symphyseal pain’ – an often overlooked cause.
- Allay understandable anxieties as appropriate – particularly regarding the well-being of the foetus or the possibility of premature labour
- Do not be too ready to diagnose UTI on the basis of an abnormal urinalysis – contamination in pregnancy is common.
Red Flags
- Changes in anatomy may alter symptoms and signs – appendicitis is notoriously difficult to diagnose in the second trimester. If in doubt, admit.
- A woman in early pregnancy who experiences unilateral lower abdominal pain followed by light bleeding or blackish discharge has an ectopic until proved otherwise.
- Don’t overlook the diagnosis of premature labour. Women with no previous experience of labour pain might not consider this possibility.
- Placental abruption causes severe, continuous pain with a tender, hard uterus. Vaginal bleeding may be minimal. Admit immediately.
- Don’t forget pre-eclampsia as a cause of epigastric pain in the third trimester – check the blood pressure (BP) and urine.