Aspirin use for obstetric indications

• Daily low dose aspirin taken during pregnancy is likely safe with minimal maternal or fetal complications when used for the indication of prevention or delaying pre-eclampsia. 
• Aspirin use should be directed by a specialist, ensuring there are no relevant contraindications including hypersensitivity to aspirin or aspirin exacerbated respiratory disease (AERD).  High dose aspirin should be avoided.

Aspirin is a non-steroidal cyclooxygenase inhibitor with anti-inflammatory and anti-platelet effects. Cyclooxygenase isoforms 1 and 2 regulates production of prostacyclin and thromboxane A2 which has opposing effects on vascular vaso-activity and platelet aggregation. Amongst other pathophysiological factors, the imbalance of prostacyclin and thromboxane A2 metabolism is thought to be involved in the development of pre-eclampsia. This prompted the investigation of the use of aspirin for its preferential inhibition of thromboxane A2 at low doses.

Daily low dose aspirin (60-100mg) is generally considered safe and is recommended prophylaxis for women at moderate to high risk of pre-eclampsia and should be initiated between 12 and 28 weeks of gestation and continued until delivery.  It is not recommended solely for the prevention of intrauterine fetal growth restriction, spontaneous preterm birth or prior unexplained stillbirth. In the absence of risk factors for pre-eclampsia, aspirin is considered harmful during pregnancy and is only recommended for use for women with recurrent miscarriages, clotting disorders or pre-eclampsia under specialist guidance.

Aspirin is contraindicated in those with hypersensitivity to other salicylates or non-steroidal anti-inflammatory drugs (NSAID) or history of aspirin allergy.  Aspirin should also be avoided in those with aspirin exacerbated respiratory disease (AERD) or history of aspirin-induced bronchospasm. Relative contraindications include history of significant gastrointestinal and/or genitourinary bleeding and severe hepatic dysfunction.

Systemic reviews on low dose aspirin use have not shown any increased risk of haemorrhagic complications during pregnancy (Choi and Shin 2021). Similarly, the number of congenital malformations are not increased in women taking aspirin compared to the general population.

High dose aspirin however may lead to variable risk depending on the stage of pregnancy. This includes concerns for pregnancy loss and congenital malformations in the first trimester and congenital cardiac defects in the fetus and potential increased risk of intracranial haemorrhage of premature infants (Stuart et al. 1982).

Following ingestion of aspirin, salicylic acid is excreted in breastmilk in very low levels and is probably subclinical in infants. It is generally considered safe during lactation.

For further information, view the RANZCOG /New Zealand College of Midwives Guidance for Aspirin for the prevention of Pre-eclampsia