Altitude Sickness and Pregnancy: Important Things to Know

Altitude sickness is a set of symptoms that range from mild to life-threatening and that develop as a result of a person being exposed to lower than normal pressures of atmospheric oxygen (O2), during and after ascent to high altitude. This generally means more than 2,500 m (8,202 ft). It could happen if you are in an inadequately pressurized aircraft, but usually it is the result of ascending to mountain locations, without giving your body adequate time to acclimate (adapt) to the higher altitude.

Acute mountain sickness develops in 25% to 85% of people who travel to high altitude, but the percentage depends on the altitude of the starting location and on the site of arrival. For travelers at Colorado ski locations, for instance, the rate of altitude sickness is 25%, but the rate jumps to 50% for those arriving at the Himalayan mountains. It climbs to 85% for people flying directly to Mount Everest. Pregnant women are not more likely than others to develop acute mountain sickness. However, young adults are more susceptible to acute mountain sickness compared with people over the age of 50 years. This means that, if you are pregnant, you have a fairly high chance of developing altitude sickness if you ascend too quickly to high altitude, such as over the course of hours to one day. The typical scenario for this is a woman going skiing during early pregnancy, when there are no particular restrictions on activity, or a woman who travels later in pregnancy, not to ski, but to accompany others on a vacation

Altitude sickness is classified as “acute” if it develops quickly (within hours to days), due to a rapid ascent to high altitude. The symptoms of acute altitude sickness range in severity from a simple headache, to multiple symptoms, such as weakness, fatigue, dizziness or lightheadedness, insomnia, and gastrointestinal symptoms, to severe, life-threatening swelling (edema) in the brain and lungs. A very different category of altitude sickness is chronic altitude sickness, which can affect the blood, lungs, and brain of people who live at high altitude over long periods of time.

Altitude sickness is a clinical diagnosis. This means that physicians make the diagnosis based on your history and findings on the physical examination, although physicians also may require some common tests, such as a chest X-ray and a sputum sample analysis. These tests can help to rule out other conditions that can appear like altitude sickness. The physical examination also may include what’s called a mini-mental status test.

For most pregnant women, acute altitude sickness is the more relevant category of altitude sickness, since it is related to traveling to high altitude rapidly. Even so, to check a patient for chronic altitude sickness, physicians also typically order blood tests and more specialized tests of the lungs.

The most mild form of altitude sickness develops with just a headache. Slightly worse cases of the also include other symptoms that doctors will use to diagnose you, such as gastrointestinal symptoms, insomnia, fatigue, and dizziness or lightheadedness. Based on whether you report each of these sets of symptoms as “not present”, “mild”, “moderate”, or “severe”, physicians assign a value based on a point system that ranges from 0 to 3. The values will be added together, resulting in  what is called the “Lake Louise score” for severity of altitude sickness.

If you have a high Lake Louise score, you also will be tested for signs of two serious altitude complications, corresponding to to the severe end of the spectrum of altitude illness. One such complication is called High Altitude Cerebral Edema (HACE); the mini-mental status test helps physicians determine whether you have HACE. The physician also may check the retinas of your eyes with a technique called ophthalmoscopy, which can help show what is happening in the blood vessels of the brain. HACE can be fatal, but generally the main danger of HACE is that it can lead to a fatal accident during mountain climbing, hiking, or skiing, because the person loses her judgment, kind of like being drunk. In other words, HACE is a major danger for those who are climbing in places where the fastest way to descend to lower altitude is by walking down. These are not the types of locations where pregnant woman would be traveling, because the risk of being far from medical facilities is just bad as the risk of developing altitude sickness.

The other severe altitude complication for which you will be tested if your altitude sickness looks like it could be severe is called High Altitude Pulmonary Edema (HAPE). This is diagnosed based on whether you experience breathing difficulty, weakness, cough, or tightness in the chest. It’s also based on whether the physician finds signs, such as wheezing or a type of sound called crackles when listening to your lungs, or the physician finds cyanosis (bluish skin), rapid breathing, or rapid heart rate.

Acute altitude sickness may increase the risk slightly of premature labor and delivery as well as pregnancy-related bleeding problems. If you ascend to 2,500 meters and beyond, the risk of other pregnancy complications, such as blood pressure elevation, preeclampsia (high blood pressure with organ problems, such as protein in the urine), abruptio placentae (detachment of the placenta from the uterus), restricted fetal growth, and fetal death, also increases. Risks also may increase if you are dehydrated, or you engage in vigorous exercise before you get accustomed to the increased altitude. As for chronic altitude sickness, this increases the risk for pulmonary hypertension, a condition that can lead to strokes or death.

The best way to prevent acute altitude sickness is to ascend very slowly over the course of each day, and then descend to sleep at an altitude slightly lower than your highest altitude of the day, then continue the process the next day. Additionally, a medication called acetazolamide is given to help prevent altitude sickness, whereas several other drugs are given if you actually develop symptoms. A steroid drug called dexamethasone is administered to treat HACE, but your physician may offer it to you also as a preventive measure if you are at high risk for HACE because you plan to ascend relatively quickly, and/or because you plan to reach a fairly high altitude. Drugs that can be given to treat HAPE include nifedipine and a couple of different families of drugs. One group, called phosphodiesterase 5 (PED-5) –inhibitors, while another group is called beta-2 agonists. Most of these drugs are considered fairly safe during pregnancy. There is some concern about beta-2 agonists, as more studies are needed to be certain of their safety, but pregnant women are directed to take them if they are suffering from HAPE, due to the seriousness of the condition.

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.

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