Ischemic Stroke and Pregnancy: Should You Worry About a Recent Report Related to the Pfizer-BioNTech Vaccine?

Last month, there was a preprint report of a possible safety signal on the Pfizer-BioNTech vaccine against SARS-CoV2 (the virus that causes COVID-19). As a preprint, the paper had not been peer reviewed (reviewed and criticized by other researchers with expertise in the area). However, it got a lot of attention in public circles, including media publicity, before health authorities and other researchers did a deep dive into that study and others and found that there was not enough evidence, at least yet, to support the paper’s conclusions. It’s worth exploring the issue here, though, because the study at first seemed to suggest a very slight elevation in the risk for ischemic strokes, meaning interruption of blood flow in the central nervous system due to clotting. A clot can be something that grows in the location where it forms (thrombotic stroke), or it can begin with a clot that begins as a piece of a clot that in a different place and that piece got stuck in the central nervous system (embolic stroke).

Now scientists are still investigating this safety signal, there’s a good reason for pregnant women and others of reproductive age not to worry and not to change plans to get vaccinated based on this report and the publicity around it. The reason is that the signal, if it’s real, is only in older people, those age 65 years of older. Even so, you should be aware of what does cause stroke in the setting of pregnancy or in the weeks following delivery. One of such cause is COVID-19. It makes little sense to avoid COVID-19 vaccination for fear of an unlikely stroke, when those who do develop COVID-19 actually have much more of a risk for neurological complications, including stroke, as compared with young to middle age healthy people who do not develop COVID-19, but get vaccinated for protection against it.

Outside the context of COVID-19, however, there have been handful of epidemiological studies, reporting a rate of stroke affecting up to 34 pregnancy women per 100,000 deliveries. Incidence of stroke during pregnancy also has been rising during the past several years, perhaps because older women are having children than in previous eras. Your risk of suffering a stroke depends on a range of risk factors. Most strokes are ischemic strokes, the same broad category of strokes that we have been discussing in connection with the recent paper on the Pfizer-BioNTech vaccine.

The heart is the source of emboli that reach the brain, either because of heart surgery, problems with a valve on the left side of the heart (aortic valve and mitral valve), an infection of the inner layer of the heart (endocarditis), an aneurysm in the wall of the heart, or atrial fibrillation ([AF] quivering of the upper chambers of the heart without active pumping of the blood into the ventricles). Such emboli are more likely to form when a person is in a hypercoagulability state, meaning that her blood tends to form clots more easily than it should. Pregnancy is one condition that produces a hypercoagulability state. Emboli that reach the brain also can form in aneurysms and other blood vessel abnormalities (such as entities called arteriovenous malformations) along routes between the heart and brain, plus certain genetic conditions, such as sickle cell disease, entail an elevated risk for clots and emboli. Additionally, in many people, emboli generated on the right side of the heart and in veins (venous thromboembolism) can reach the left side of the heart through what is called a patent foramen ovale (PFO), an opening between the heart’s right and left atria. The foramen ovale that is present in everybody during fetal life and that closes soon after birth, but possibly as many as one third of all people have a PFO. Additionally, there is a severe pregnancy complication called an amniotic fluid embolism (AFE). Although AFE is not only an embolism, because it produces an immune response to amniotic material in the mother’s bloodstream, it can lead to a cerebral embolism.

A stroke can produce temporary or permanent disability and even can be fatal. Disabilities that often occur in strokes include problems with speech or understanding of speech, paralysis of parts of the body, such as the face, arms, or legs. Typically, one side of the body or face is affected. In cases of ischemic stroke, medications are given to restore blood flow to the affected area of the brain and to prevent additional emboli from forming and reaching the brain. Quick recognition of the stroke is extremely important and is a major factoring in determining the treatment. The gold standard treatment consists of drugs of a category called fibrinolytic (or thrombolytic) agents, which are given to break up the clot. In particular, a clot busting agent called tissue plasminogen activator (tPA) is given, but it is effective only if you receive it within approximately 4.5 hours of the onset of the stroke. The drug can be given intravenously, or endovascularly, meaning through an instrument in a catheter that is inserted into a vein. Although tPA is considered to be a risk for the fetus, it has been administered successfully in pregnancy and the risk must be weighed against the risks and benefits of giving the drug and the risk of not giving it.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

Leave a Reply