Recently a journalist conducted a simple, observational scientific study. Standing at an intersection in Palo Alto, California by the entrance to Stanford University, he observed people riding bicycles over the course of a few hours. After doing this while jotting down the numbers of cyclists wearing helmets, masks, both, or neither, he got an interesting result. Of roughly 400 cyclists that he observed during those few hours, 41 percent were wearing masks, while just 17 percent were wearing helmets. Probably, I do not need to point out that Stanford University is the home of some of the greatest brains on planet Earth and that the cyclists —all of whom are required to have received three vaccine doses against SARS-CoV2 (the virus that causes COVID-19) in order to be on campus— were riding their bikes outdoors, where the virus is easily swept away by the air and where the surfaces of streets, sidewalks, and curbs, are made of concrete.
What does this tell us about how people in our society balance risks? It tells us that people often develop very distorted ideas of risk. This is something that can we explore in the context of pregnancy, both in connection with COVID-19, but also in connection with other health topics. One particular area in which people often act based on very distorted understandings of risk radiation health. We touched this topic three years ago here on The Pulse in a story the health issues of flying when you are pregnant. Are you worried about flying while pregnant on account of the fact that flying exposes you and your fetus to ionizing radiation from cosmic rays and solar particles resulting in radiation dosage higher than what you normally receive on the ground? You shouldn’t worry, because, even on a flight with the highest radiation exposure —a long distance flight taking you through higher latitudes— the dosage of ionizing radiation that you accumulate on the flight is not high enough to pose any danger. Judging by the fact that many pregnant women take such flights, seemingly without much though to high altitude radiation, this part of the risk is probably clear. But now, how about x-ray scans given to randomly selected people at security. Are you one of the many people who, when selected for such a security check, opt for a hand pat-down in order to avoid the x-rays? Or do you opt out of the x-ray scan, particularly when you are traveling pregnant? If you do opt out, but you do not opt out of flying at all, the your risk assessment would be off. Here is why. That radiation dosage from the flight at high latitudes, at typical cruising altitudes, that’s the equivalent of getting about one to two chest x-rays worth of ionizing radiation for each hour in the air, or about 10 chest x-rays or so for a long flight, such as between New York and Tokyo. If you are comfortable with the idea that this is not enough to put your fetus at risk, now consider that the radiation dosage from the security scan is orders of magnitude lower than the not dangerous dose that you receive in the air.
The scanner employs such low power x-rays that they bounce off your body. The security people don’t want to see through your body. They only want to see through your clothing to be able to detect a concealed weapon. The take-home message is that it makes no sense to be scared of the radiation from the security scanner, yet not be scared of the radiation that you receive each hour in the air. Being scared of the radiation from the scanner is like being scared of the normal background ionizing radiation that you are receiving right now as a result of living on the surface of the Earth. Now let’s extend this to one more thing. If you are not worried about receiving a chest X-ray or two of ionizing radiation in the air, how about a diagnostic test using low dose x-rays on the ground? A half century ago, it was common for obstetricians to order pelvic x-rays on pregnant women to evaluate them for what doctors call cephalopelvic disproportion. This is a condition in which the baby’s head is too big for a safe vaginal delivery, so it’s an indication for a cesarean birth. Today, pelvic x-rays are not needed so much, because there is ultrasound, but actually the x-rays are more accurate for taking such measurements, because they are particularly good for imaging bone. And there is no rationale for avoiding such radiographs in pregnancy, as long as we are talking about simple flat film radiographs, which impart very low radiation dosage. This is different from certain other imaging modalities, notably computed tomography (CT) scanning. Unlike simple radiographs, such as a flat film x-ray, or dental x-rays, CT involves a machine that take many different x-ray scans from different angles and then a computer algorithm puts everything together into a three-dimensional image. Radiologists can then view the part of the body scanned in slices. Depending on what parts of the body is scanned (including the entire body) and the power of the CT scan, the radiation dosage can be substantially higher than the radiation dosage from a simple radiograph, like a chest X-ray. Sometimes CT scanning is done at low power, such as to screen smokers on a regular basis for signs of lung cancer. But any time that doctors consider doing a CT on a pregnant women, it’s usually to evaluate her for something urgent, in which case higher power is needed. This is the usual situation with CT and it involves ionizing radiation doses on a level that do entail some risk to the fetus, so it becomes a question of balancing the risks doing the test against the risks of not doing the test. The point here is that a simple chest x-ray, a dental x-ray, and even a pelvic x-ray do not impart anything close to the radiation dosage of a CT, so there’s not even an issue of possible risk to the fetus.
But you wouldn’t know this seeing how healthcare systems behave when it comes to X-rays during pregnancy. Dentists today generally have stopped using lead aprons while X-raying the mouths of patients who are not pregnant, for a good reason. Modern X-ray beams are very focussed, so the x-rays go only where they are needed. They don’t go near your womb. And yet, if you get dental x-rays as a pregnant women, then often you will be given the apron. Similar decisions are made in obstetrical practices. Society has a distorted fear of low dose radiation and medical practice accommodates this fear, not because it makes sense scientifically, but rather…you guessed it…because of legal considerations. If you are imaged while pregnant and then, for whatever reason, anything goes wrong with the baby, lawyers could be making trouble. Somehow, the same thing does not happen when pregnant women are exposed to safe radiation levels while flying.
As for flying though, while you need not worry about the radiation, there is actually a health issue that is significant when you fly pregnant, especially during the late part of pregnancy and in the six weeks or so following delivery. Your blood is particularly prone to for clots. This means that being pregnant, or recently pregnant, sitting down for long flights puts you at risk of what’s called venous thromboembolism (VTE). This is a reason not to take long flights during the second half of pregnancy, or when you have recently delivered, and if you cannot avoid such travel, you should try to move your lower body. Get up and walk through the aisle when there is an opportunity and also do exercises in your seat. You really want to avoid VTE, which can begin with a clot in a vein in your leg or pelvis and can advance to a worse complication called a pulmonary embolism. And by the way, if doctors suspect that you may have a pulmonary embolism they need to do an imaging test on your lungs, a test that exposes you to radiation.
Returning to the mask topic that we used to open our story today. Let’s not forget that masks were vital to slowing the spread of the virus throughout most of the COVID-19 pandemic. Pregnant women are at particular risk of developing a severe course of COVID-19 and at risk of pre-term birth. But vaccinated pregnant women are in very good shape when it comes to the COVID-19 risk. You can go bicycling safely while pregnant without a mask. But please, wear a helmet.