There are four populations to consider when determining the safety of high-altitude during pregnancy:
Pregnant women who live at high altitudes
Pregnant women who live at high altitudes and exercise
Pregnant women who visit high altitudes
Pregnant women who visit high altitudes and exercise
Research has demonstrated a difference between residents and visitors, with residents associating with more adverse outcomes; however, if a woman is used to living at high altitude, to include generations before her, this appears to be a strong, protective influence against these outcomes.
There is significantly more research on pregnant women residing at high altitudes that those who visit. Therefore, most safety information is based on studies regarding non-pregnant individuals added to what is currently known about pregnancy-related changes on the body that could impact pregnant women and/or their babies at high altitude.
Exposure to altitude results in decreased blood oxygen saturation (there is less oxygen in the blood); the body begins to make changes to compensate – known as acclimatization (the same process occurs during air travel, albeit to a lesser extend due to cabin pressurization).
Oxygen blood saturation: measure of the percentage of oxygen in the blood; measured by a device that goes on the finger (pulse oximetry).
The definition of “normal” varies, but is often indicated at 95% to 100%, with “abnormal” beginning at less than 95%.
Acclimatization: the process in which the body adapts to a major change in its environment; can occur through altitude as well as temperature.
Most people acclimate to high altitudes without complications, but the process takes time, and pregnant woman and their co-travelers need to schedule about 3 to 5 days for proper acclimatization.
The acclimatization process within the body mainly consists of short-term hyperventilation (breathing faster) and increased red blood cell mass, which helps carry additional oxygen throughout the body.
If individuals cannot acclimate, they can suffer from a high-altitude disease, such as acute mountain disease (AMS), high-altitude pulmonary edema, high-altitude cerebral edema, or chronic mountain sickness.
AMS is the most common, presenting most often with a headache (2 to 12 hours after arrival) sometimes accompanied by fatigue, loss of appetite, nausea, and occasionally vomiting. AMS generally resolves within 12 to 48 hours of acclimatization. Pregnant women should be hypersensitive to the onset of these symptoms, especially since they mimic common pregnancy-related symptoms; this can help avoid a delay in medical assistance.
Some individuals are more susceptible to high altitude diseases than others (mostly genetic), therefore the incidence of these diseases is variable and cannot be predicted, especially in first-time exposure.
It is possible a pregnant woman exposed briefly or permanently to high altitudes may have an increased risk of complications compared to a pregnant woman at sea level, but research is limited. This assessment is based on possible oxygen-related changes that alter blood flow to the uterus, placenta, and umbilical cord, impacting nutrient supply to the fetus.
Pregnancy-related blood volume changes include an increase in red cell mass, which provides greater oxygen to the fetus (i.e. the body is already undergoing an "acclimatization" process). This increase helps compensate for any decrease in the mother’s oxygen saturation during high-altitude travel.
Despite the above, numerous high-attitude studies have shown that chronic hypoxia (lack of oxygen) in the fetus is associated with intrauterine growth restriction, reduced birth weight, a need for supplemental oxygen at birth, and the mother’s development of preeclampsia, the latter likely due to vascular changes as a result of decreased oxygen.
A survey of Colorado obstetricians indicated that preterm labor and bleeding were the most encountered complications among high-altitude pregnant visitors; the mechanism for why these complications occur is not known.
A study published in September 2021 of a pregnant cohort in Ecuador documented higher complications among high-altitude newborns. Complications included hematological and arterial blood gases parameters (pH and levels of oxygen and carbon dioxide in the blood).
To date, the most common birth complication observed in those who reside in high altitudes is low birth weight as a result of slow growth. Other complications include heart rate changes and preeclampsia (as stated above).
In uncomplicated pregnancies, altitudes up to 2,500 miles (4,023 km) are well tolerated by both mother and fetus. However, there is a lack of information regarding the safety of altitudes higher than 2,500 miles, as well as guidance to avoid complications. It is advised, however, that pregnant women should not exceed 2,500 miles in the first 4 to 5 days of short-term exposure.
Note: In pregnant women with underlying conditions or specific risk factors, concern over high-altitude travel is warranted. Pregnant women who wish to travel to high altitudes need to discuss this with their HCP, especially in women who smoke, have hypertension, preeclampsia, respiratory or cardiac disorders, sleep apnea, threat of preterm labor, placental problems, or preexisting low blood oxygen saturation.
Although mother and fetus compensate well to brief periods of less oxygen, exercise at high altitudes can place a strong additional burden on oxygen requirements.
Although data is limited, in uncomplicated pregnancies, pregnant women and their babies appear to tolerate exercise well. However, short-term abnormalities in fetal heart rate have been observed. It is critically important that women who wish to exercise at high altitudes acclimate and hydrate property to avoid sickness and talk to their HCP first.
Women should talk to their HCP regarding any questions or concerns they have about high-altitude living and/or travel during pregnancy, as well as before traveling to high altitudes, especially for the first time.
Pregnant women who travel to high altitude locations should have a plan. Prepare for a longer trip, take time acclimating, remain hydrated, and have a map/route to a local hospital should complications arise. Higher altitude locations may be quite a bit away from medical care.
Women who reside at high altitude locations, or move to a high altitude location during pregnancy should talk to their HCP about any concerns they have regarding the health of their pregnancy/baby.
For women concerned about altitude in relation to air travel, read more here.
Partners, family members, or friends should make accommodations to their trip to high altitude locations if they are traveling with a pregnant woman.
Pregnant women and their co-travelers need to schedule at least 3 to 5 additional days to their trip for the acclimatization process. This will help avoid complications that arise from a fast decrease in blood oxygen saturation. This is especially important prior to exercise at high altitude, which demands a significant amount of additional oxygen.