Acetylsalicylic Acid

Revised March 4, 2019

Section 1.1

Midwives may independently prescribe, order and administer this drug.

Acetylsalicylic Acid (ASA) is an analgesic, antiplatelet agent and non-steroidal anti-inflammatory (NSAID).

Indications and Clinical Use:

Full-dose ASA (>162mg/day) should be avoided during pregnancy and breastfeeding due to an increased risk of hemorrhage. However, low-dose ASA during pregnancy has been shown to reduce the frequency of preeclampsia by approximately 10-20%, as well as associated adverse pregnancy outcomes, for those at higher risk of the disease. This is thought to be related to its effect on platelet thromboxane synthesis, vascular wall prostacyclin synthesis and modulation of inflammation.

A review of the literature suggests the following non-exhaustive list of risk factors for preeclampsia in a current pregnancy: previous pre-eclampsia, chronic renal disease or proteinuria, antiphospholipid antibody syndrome, preexisting diabetes mellitus, pre-existing hypertension, or multiple additive factors (nulliparity, maternal age >40, multiple pregnancy, abnormal placental analytes, previous unexplained stillbirth, abnormal uterine artery doppler studies, IUGR, cocaine or methamphetamine use, smoking, obesity, invitro fertilization, previous miscarriage with same partner, family history of preeclampsia, subsequent pregnancy with a new partner, interpregnancy interval >10 years, vaginal bleeding in early pregnancy).

Low-dose ASA is most effective when started between 11 and 16 weeks gestational age but may be started any time prior to 36 weeks.


Hypersensitivity to NSAIDs, asthma, rhinitis, nasal polyps.

Warnings and Precautions:

Assess for potential drug interactions before prescribing. Use with caution in patients with platelets and bleeding disorders. Patients with nasal polyps, sensitivity to tartrazine dyes and asthma may have an increased risk of salicylate sensitivity. Discontinue if tinnitus occurs.


Low Dose – Compatible
Full Dose – Human Data Suggest Risk in 1st and 3rd Trimesters


Limited Human Data- Potential Toxicity

Adverse Reactions:

Adverse effects of aspirin are rare at low dosages, but may include hemorrhage at any site, urticaria, ulcer, cardiac arrhythmia, cerebral edema, coma, confusion, dizziness, fatigue, headache, Reye’s syndrome, lethargy, nervousness, hepatotoxicity, anemia, heartburn, nausea, vomiting, asthma and tachypnea, among others.

Dosage and Administration:

Low-dose ASA (81-162mg) OD PO at bedtime, from as early as 11 weeks until 36 weeks gestational age. Consider taking with 1 gram of calcium PO.