Low-Dose Aspirin and Conception
Low-dose aspirin may help with conception by improving uterine and ovarian blood flow, enhancing implantation rates, and potentially reducing pregnancy loss, particularly when started before conception in women with infertility or recurrent pregnancy loss. 1
Mechanisms of Action for Conception
Low-dose aspirin (typically 81-100 mg daily) may improve conception through several mechanisms:
Improved blood flow: Aspirin increases blood flow velocity in uterine and ovarian arteries with lower pulsatility index values, which can enhance the implantation environment 1
Enhanced implantation: Studies in women undergoing in vitro fertilization have shown that preconception low-dose aspirin is associated with improved implantation rates 1
Balanced prostanoids: Low-dose aspirin balances thromboxane A2 (vasoconstrictive) and prostacyclin (vasodilatory) levels, maintaining adequate uteroplacental blood flow and potentially improving placentation 2
Reduced inflammation: Aspirin may help modulate inflammatory factors that affect the endometrium and uterine/ovarian vasculature prior to pregnancy 1
Evidence for Preconception Use
Research suggests that starting aspirin before conception may be beneficial:
Randomized controlled trials have shown that preconception initiation of 75-100 mg aspirin is safe in pregnancy 1
The Effects of Aspirin in Gestation and Reproduction (EAGeR) trial specifically studied preconception-initiated low-dose aspirin in women with one to two prior pregnancy losses 3
A systematic review evaluating low-dose aspirin initiated prior to conception or before 11 weeks in women with infertility or recurrent pregnancy loss showed a significant decrease in preterm birth <37 weeks (5.3% vs. 10%, RR 0.52, CI: 0.27-0.97, p=0.04) 1
Optimal Dosage and Timing
Dosage: Most guidelines recommend 81 mg (US) or 75-162 mg (Canadian/ISSHP) daily 4
Timing: For conception benefits, starting before pregnancy appears beneficial 1, 2
Duration: If pregnancy occurs, aspirin is typically continued until 36 weeks gestation 5
Cautions and Considerations
Low-dose aspirin should be considered primarily for women with risk factors for preeclampsia or those with infertility/recurrent pregnancy loss 1, 5
Common pitfalls include:
- Starting aspirin too late (after conception or after 16 weeks) may reduce effectiveness 4
- Using aspirin without appropriate indication may expose women to unnecessary risks
- Discontinuing too early may reduce benefits
While generally safe, aspirin should be used with caution in the last trimester due to potential bleeding risks 4
Who May Benefit Most
Low-dose aspirin for conception may be most beneficial for:
- Women with previous pregnancy losses 3
- Women with infertility undergoing IVF 1
- Women with conditions affecting placentation (chronic hypertension, autoimmune diseases) 1
- Women with risk factors for preeclampsia who are trying to conceive 1, 5
For women with recurrent pregnancy loss or infertility, the evidence suggests that preconception low-dose aspirin may improve outcomes by enhancing implantation and early placentation, potentially leading to better pregnancy outcomes.