The question of whether it is safe to use low-dose aspirin during pregnancy is a common one for expectant parents. While often referred to as “baby aspirin,” it is a medication that requires careful medical consideration, not a supplement for general use. Low-dose aspirin (LDA) is generally considered safe and beneficial when a healthcare provider prescribes it to address specific risks. Its use during pregnancy is a targeted medical intervention, and it must only be taken under the direct guidance of an obstetrician or other prenatal care specialist.
Defining Low-Dose Aspirin Use in Pregnancy
The aspirin used in pregnancy is specifically a low-dose formulation, most commonly 81 milligrams (mg) daily, though some protocols may recommend up to 150 mg. This dosage is substantially lower than the standard 325 mg tablet typically used for pain relief or reducing fever, which is generally discouraged during pregnancy. At a low dose, aspirin acts primarily as an antiplatelet agent, whereas higher doses provide anti-inflammatory effects.
Aspirin, or acetylsalicylic acid, works by irreversibly inhibiting an enzyme called cyclooxygenase-1 (COX-1) in platelets. By inhibiting COX-1, the medication prevents platelets from producing thromboxane A2, a powerful substance that promotes blood clotting and constricts blood vessels. This action reduces the tendency of platelets to aggregate, effectively “thinning” the blood in a controlled way.
The goal of this antiplatelet effect is to improve blood flow through the placenta, which is the organ providing oxygen and nutrients to the developing fetus. In pregnancies where placental development or function is compromised, this improvement in blood flow can help prevent serious complications.
Primary Medical Indications for Prescription
Low-dose aspirin is not recommended for all pregnant individuals but is prescribed specifically for those identified as having an elevated risk of certain complications. The most significant indication is the prevention of pre-eclampsia, a condition characterized by new-onset high blood pressure and signs of damage to another organ system, typically after 20 weeks of gestation. Individuals with a history of pre-eclampsia in a previous pregnancy are considered to be at high risk.
Other factors that significantly increase the risk for pre-eclampsia include carrying multiple fetuses, having chronic conditions like type 1 or type 2 diabetes, chronic hypertension, or kidney disease. Autoimmune disorders, particularly Antiphospholipid Syndrome (APS), which involves abnormal blood clotting, are also strong indications for LDA therapy. Treatment can reduce the likelihood of pre-eclampsia by 24% and the risk of severe pre-eclampsia even more significantly.
Low-dose aspirin also demonstrates a beneficial effect in reducing the risk of Intrauterine Growth Restriction (IUGR), where the fetus does not grow to its expected potential. This is thought to be a direct result of the improved placental blood flow facilitated by the aspirin’s antiplatelet action. By optimizing the delivery of nutrients and oxygen to the fetus, LDA helps support healthy development and contributes to a lower risk of preterm birth in these high-risk populations.
Timing and Duration of Treatment
The effectiveness of low-dose aspirin as a preventive treatment relies heavily on the timing of its initiation. For the prevention of pre-eclampsia, the medication must be started early in the pregnancy to have the maximum therapeutic effect. Guidelines recommend beginning daily LDA treatment between 12 and 16 weeks of gestation.
Starting the regimen optimally before the 16th week allows the medication to influence the initial development of the placenta and the remodeling of the uterine blood vessels. Studies show that starting treatment later than 16 weeks significantly reduces the protective effect against pre-eclampsia and IUGR. Consistent daily adherence is necessary to maintain the continuous antiplatelet effect.
The duration of treatment typically continues throughout the remainder of the pregnancy. Many healthcare providers recommend discontinuing the medication around 36 weeks of gestation as a precaution against a slightly increased risk of bleeding during delivery. Some practitioners, however, may advise continuing until the time of birth if the risk of pre-eclampsia remains high.
Potential Maternal and Fetal Risks
When taken at the prescribed low dose, the risk of serious complications for both the mother and the fetus is considered low. Maternal side effects are usually minor and include mild gastrointestinal upset or an increased tendency for bruising. Low-dose aspirin does not appear to increase the risk of major obstetric complications like placental abruption or postpartum hemorrhage.
The primary concern historically associated with aspirin in pregnancy involves the use of high doses late in the third trimester. High-dose aspirin can cause the premature closure of the fetal ductus arteriosus, a blood vessel that is naturally open during fetal life. This risk is specifically linked to the higher, anti-inflammatory doses of aspirin and is avoided by using the low-dose regimen in the second and third trimesters.
Some individuals should not take low-dose aspirin because of contraindications. These include a known allergy to aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs), or having a pre-existing bleeding disorder. For the vast majority of patients with appropriate indications, the benefits of preventing severe complications outweigh the minimal risks associated with controlled low-dose therapy.