Low-dose aspirin use in the first trimester of pregnancy and risk of birth defects

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Aspirin is often recommended in pregnancies at moderate and high risk of preeclampsia (PE). It reduces the risk of PE by improving placentation, preventing platelet aggregation and reducing endothelial inflammation (inhibiting thromboxane A2 synthesis).

National and international protocols recommend daily use at low doses (< 150 mg) and starting before 16 weeks. And in some situations, such as in antiphospholipid antibody syndrome (APAS), as soon as pregnancy is diagnosed.

Read also: Delayed clamping of the umbilical cord in diabetics may increase the risk of hyperbilirubinemia in neonates

And because aspirin crosses the placental barrier, there is a great deal of interest and concern in the medical community about its effects in the first trimester, especially with regard to teratogenicity.

Aspirin remains an effective treatment to prevent cardiac events.


A meta-analysis was published this month in International Journal of Gynecology and Obstetrics with the aim of collecting randomized clinical trials and evaluating the risk of birth defects when using aspirin in the first trimester.

The systematic review included randomized controlled trials with pregnant women who were exposed to low-dose aspirin or placebo or no intervention during the first trimester, defined as before 14 weeks of gestational age.

Eight studies meeting the inclusion criteria were included. These studies included 7,564 participants who received aspirin and 7,670 participants in the control group (placebo or without intervention).

Aspirin doses ranged from 75 to 150 mg across studies, and onset of use ranged from preconception to 14 weeks and zero days of gestational age.

The overall incidence of congenital anomalies was 0.74% (56/7564; 95% CI: 0.57%, 0.96%) in women exposed to aspirin and 0.88% (68/ 7670; 95% CI: 0.69%, 1.12%) in women in the control group. There was no difference or increased risk of birth defects in women who used aspirin (OR 0.87, 95% CI 0.62, 1.23).

Even when the analysis only included studies that had been exposed to aspirin during the embryonic period (<9 weeks), the result was consistent with the overall conclusion (OR 0.97, 95% CI: 0.56, 1.69).


Despite the limitations of this meta-analysis and the included studies, the authors concluded that the use of low-dose aspirin during the first trimester does not increase the risk of birth defects compared with the administration of placebo or no intervention. However, they suggest that more studies should be directed towards this theme.

Additionally, the use of high doses or in women at high risk for birth defects, such as those with diabetes, has not been evaluated and warrants further attention in the future.


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