What are the guidelines for Acetylsalicylic Acid (ASA) use in pregnancy in Alberta?

Guidelines for ASA Use in Pregnancy in Alberta

Low-dose acetylsalicylic acid (ASA) at 75-100 mg/day is recommended prophylactically for pregnant women with a history of early-onset (<28 weeks) pre-eclampsia, and should be administered at bedtime, starting pre-pregnancy or from diagnosis of pregnancy, but before 16 weeks gestation, continuing until delivery. 1

Indications for ASA in Pregnancy

Prevention of Pre-eclampsia

• Low-dose ASA (75-100 mg/day) is indicated for women with:
  • History of early-onset pre-eclampsia (before 28 weeks gestation)
  • High-risk factors for developing pre-eclampsia
  • Abnormal uterine artery Doppler studies indicating placental dysfunction

Timing of Initiation

• Most effective when started:
  • Before pregnancy (if planning pregnancy)
  • As early as possible after pregnancy diagnosis
  • Before 16 weeks gestation 1
  • Starting ASA ≤16 weeks shows significantly better outcomes (RR 0.48) compared to starting at ≥20 weeks (RR 0.82) 2

Dosing

• Recommended dose: 75-100 mg daily
• Best administered at bedtime to optimize effectiveness
• Continue until delivery

Special Populations

Inflammatory Bowel Disease (IBD)

• For pregnant women with IBD on 5-ASA maintenance therapy, continuation throughout pregnancy is recommended 1
• Meta-analyses show 5-ASA use during pregnancy is not associated with significant increases in:
  • Congenital abnormalities
  • Stillbirth
  • Spontaneous abortion
  • Preterm delivery 1
• For women with ulcerative colitis taking 5-ASA formulations containing dibutyl phthalate (DBP), switching to a non-DBP containing formulation before conception is recommended 1

Antiphospholipid Syndrome

• Low-dose ASA in combination with subcutaneous heparin is recommended to increase chances of full-term delivery 3
• For ASA-sensitive patients with antiphospholipid syndrome, ASA desensitization may be considered under careful monitoring 3

Safety Considerations

Third Trimester Concerns

• ASA should be used with caution during the last trimester of pregnancy as it may cause:
  • Problems in the unborn child
  • Complications during delivery 4
  • Prolonged gestation and labor
  • Increased blood loss during delivery 5

Contraindications

• Known ASA allergy (unless desensitization is performed)
• Active peptic ulcer disease
• Bleeding disorders

Monitoring

• Regular blood pressure monitoring
• Uterine artery Doppler studies as indicated
• Assessment for signs of pre-eclampsia at each prenatal visit

Practical Implementation

1. Identify high-risk women early, ideally pre-conception
2. Start low-dose ASA (75-100 mg) at bedtime before 16 weeks gestation
3. Continue through pregnancy until delivery
4. Supplement with adequate folic acid (2 mg/day) if using sulfasalazine for IBD 1
5. Consider discontinuation 1-2 weeks before anticipated delivery if concerns about bleeding risk

Caveats and Pitfalls

• Starting ASA after 20 weeks gestation shows limited benefit in preventing pre-eclampsia
• Unnecessary exposure to ASA should be avoided in the first trimester despite relatively low risks 5
• ASA sensitivity requires special consideration - desensitization protocols may be needed for high-risk patients who would benefit from ASA therapy 6
• Avoid high-dose ASA formulations during pregnancy

ASA remains an important preventive therapy for high-risk pregnant women when started early, with the benefits of preventing pre-eclampsia, intrauterine growth restriction, and associated complications outweighing the potential risks when used appropriately.