First Trimester Abdominal Pain

First trimester abdominal pain is pain in the lower or upper abdomen before 13 weeks of pregnancy. Causes are pregnancy related (miscarriage, ectopic pregnancy, corpus luteum cyst, round ligament stretching) and unrelated (appendicitis, urinary tract infection, constipation, gastroenteritis, ovarian torsion). It matters because ectopic pregnancy and appendicitis are life-threatening and easy to miss.

• Mild bilateral cramping is common and often benign.
• Risk factors for ectopic pregnancy: previous ectopic, pelvic infection, tubal surgery, intrauterine contraceptive device.
• Pain with a positive pregnancy test is ectopic pregnancy until excluded.

Presentation depends on cause: cramping with bleeding suggests miscarriage; unilateral pain with shoulder tip pain suggests ectopic pregnancy; right iliac fossa pain with vomiting suggests appendicitis; dysuria suggests urinary infection.

• Check pulse, blood pressure, temperature and abdominal tenderness or guarding.
• Pelvic examination for cervical excitation, adnexal mass and os.
• Differential diagnosis: ectopic pregnancy, threatened or incomplete miscarriage, corpus luteum cyst, ovarian torsion, appendicitis, urinary tract infection, pyelonephritis, constipation.
• Complications: haemorrhage, shock, peritonitis, sepsis, loss of ovary or tube, pregnancy loss.

The approach is to confirm pregnancy, locate it, and exclude surgical causes.

• Urine pregnancy test, haemoglobin, full blood count, blood group and Rhesus status.
• Transvaginal ultrasound for sac location, adnexal masses, free fluid and ovarian size.
• Urine dipstick and microscopy; malaria test in endemic areas; serum hCG if the sac is not seen.
• Graded compression ultrasound of the right iliac fossa for suspected appendicitis; magnetic resonance imaging if available and unclear.
• Serum lactate and creatinine if the patient is unwell.

The principle is to find and treat the cause, and not to withhold imaging or surgery because of pregnancy.

• Supportive: oral or IV fluids; Ringer's lactate 1 litre if dehydrated or unstable; rest; fasting if surgical cause is suspected.
• Pharmacological: paracetamol 1 g oral or IV 6-hourly as needed (maximum 4 g in 24 hours); avoid ibuprofen and other NSAIDs; morphine 2.5 to 5 mg IV titrated for severe pain; for urinary infection give cefalexin 500 mg oral 6-hourly for 7 days; for appendicitis give ceftriaxone 2 g IV once daily plus metronidazole 500 mg IV 8-hourly before surgery; for ectopic pregnancy give methotrexate 50 mg/m2 IM as a single dose if stable and hCG is below 5000 IU/L; for constipation give lactulose 15 mL oral twice daily.
• Procedures: laparoscopic salpingectomy for ectopic pregnancy; appendicectomy for appendicitis; detorsion for ovarian torsion.
• Special groups: Rhesus negative women with bleeding or surgery give anti-D immunoglobulin 250 IU IM within 72 hours.
• Red flags: shoulder tip pain, syncope, rigid abdomen, pulse above 110 per minute, fever above 38 degrees Celsius, vomiting with localised tenderness.
• Follow-up: review at 24 to 48 hours; repeat scan and hCG if no diagnosis; arrange antenatal booking once an intrauterine pregnancy is confirmed.