Ask the Flight Surgeon / By MAJ (Dr.) Douglas R. Hogoboom and Dr. Michael T. Acromite: Q: Hey doc, I am considering becoming pregnant. How would pregnancy affect my flight status?
FS: First of all, thank you for a very important question. Many pregnant women have safely flown during pregnancy, but there are risks that must be considered. The aviation environment presents various exposure risks (noise, vibration, temperature changes, decreased oxygen, G-forces, toxic gases, etc.). These environmental changes are known to affect the mother and baby, but the extent of adverse effects remain uncertain. This uncertainty stems from research restrictions for ethical reasons. However, reviews of human pregnancy outcomes after natural, incidental, or accidental exposures in the aviation and non-aviation environments provide valuable information. Animal studies also provide additional information. Pregnancy experiences in aviation across services is also reviewed for safety. The U.S. Army Aeromedical Activity (AAMA) has issued an Army Pregnancy Aeromedical Policy Letter (APL) based on current Army Policy and available pregnancy and safety information.
A normal pregnancy lasts about 40 weeks divided into three separate trimesters, each lasting about three months. Each trimester has various expected changes, milestones, and risks for the mother and the baby. The first trimester is the baby’s most susceptible time and critical for organ system development. This time poses the highest risk of miscarriage from either natural or environmental causes. Miscarriages are less common in the 2nd and 3rd trimesters, but exposures still may cause preterm labor, premature delivery, or other events.
Throughout pregnancy, physiology, medical, and exposure risks change. The mother’s physiology changes to support fetal development and growth. These include changes in hormones, blood, heart function, blood pressure, lungs, vision, and clotting mechanisms. These changes are common and considered ‘normal’ for pregnancy, but they can induce unexpected risks for pregnant aviators.
Hormone changes can cause nausea and vomiting, known as morning sickness. This can be painful and distracting to aircrew, and may require medications that are not safe for aviation. Fortunately, this generally occurs in the first trimester and resolves in the 2nd trimester.
The mother’s blood pressure is lower during pregnancy due to the placental flow and blood vessel relaxation. This lower blood pressure makes “passing out” more common and a risk in aviation. Others experience dangerously high blood pressure known as gestational hypertension. This can affect the placenta and fetal growth and may require medication. When it impairs the mother’s kidneys or other organs, it is called preeclampsia. Symptoms of preeclampsia can include headache, vision changes, abdominal pain, and altered mental status, which concern aviation safety. This condition can even result in seizures, called eclampsia, which is certainly dangerous for aviation.
The mother’s fluid and blood volume increase to provide more blood to the placenta for the baby. Fluid changes can cause swelling. Swelling and body changes can cause discomfort, alter safety equipment fit, or affect safe egress. Swelling can also affect the mother’s corneas and visual acuity.
The mother’s plasma (watery part of blood) increases more than her red blood cells (oxygen carrying cells) causing her blood to be thinner. This is commonly called “anemia of pregnancy.” Although often considered a “normal” part of pregnancy, this anemia may result in fatigue, shortness of breath, vision changes, and even “passing out,” all dangerous in aviation.
During pregnancy, the mother’s blood clots more easily. This begins early in pregnancy, increases throughout pregnancy, and continues until six weeks after delivery. The greatest risk of clots occurs near delivery and shortly afterward. This naturally helps to reduce blood loss at delivery, but dangerous clots can rarely occur unexpectedly.
The fluid dynamics of pregnancy also affects the lungs and kidneys. The mother’s breathing patterns change, the lungs are more apt to collect fluid, and pneumonia is more common. The kidneys produce more urine causing frequent urination, and both the bladder and kidney are more susceptible to infection.
The hormones of pregnancy affect the mother’s insulin and blood sugar, and interfere with insulin, resulting in higher blood sugar levels. While usually good for growing babies, the effect can cause very high blood sugar levels dangerous for the mother and baby. When abnormally high, this is called gestational diabetes. In most cases, these changes can be managed by your provider. However, possible symptoms such as increased urination, vision changes, fatigue, and “passing out” are concerning in aviation.
Noise and vibrations in aviation may pose risk to the mother and baby. Hearing organs develop at 18-20 weeks and may be susceptible. The mother’s skin, muscles, uterus, and placenta may decrease exposure as found in animal studies, but this is still to be confirmed in humans. Some research also suggests that vibrations may be associated with premature labor or growth restriction in non-aviation environments, but this has not been clarified for aviation.
Pregnancy can worsen or change the treatment of medical conditions present before pregnancy such as anemia, hypertension, thyroid disorders, diabetes, psychiatric conditions, and others. These are important when an aviator has a flight waiver, but then becomes pregnant.
The Army Pregnancy APL considers these risks. Extra precautions are taken to protect the flying mother and baby with certain flight restrictions. Only flight simulators are allowed up to 12 weeks due to susceptibilities and risk of ectopic (tubal) pregnancy, and after 25 weeks due to pregnancy and delivery risks. From 12 to 25 weeks, aircrew are able to fly multi-engine, non-ejection seat, dual pilot aircraft at less than or equal to 10,000’ (above sea level) cabin altitude. The dual piloted aircraft restriction addresses the unpredictable nature of pregnancy conditions, physiological changes, and risk of blood clots, “passing out,” and vision changes. The cabin altitude restriction assures adequate oxygenation for mother and baby. Finally, from 25 weeks to delivery, flight duties are not authorized due to the increasing risk for premature labor, rupture of membranes, bleeding, clots, and preeclampsia. By six weeks after delivery, these risks are resolved.
Flight time during pregnancy requires your flight surgeon/aeromedical physician assistant (FS/APA) to ensure you understand the potential risks and safety restrictions. Pregnancy complications will be addressed by your FS/APA with information from your pregnancy provider.
Aside from the Army, U.S. military services generally consider pregnancy as disqualifying for flight duty and require a waiver due to different aircraft types and various associated risks. In the U.S. Army, a fully trained aviator with a normal uncomplicated pregnancy is not disqualified following the published safety restrictions. However, you must still notify your FS/APA, continue with pregnancy providers, and follow guidance from your FS/APA and Army Pregnancy APL. Also, you must notify your FS/APA of any medical changes or complication during the pregnancy, as they may require additional attention, waiver, or grounding for safety.
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This article was supported in part by an appointment to the Research Participation Program at the U.S. Army Aeromedical Activity (AAMA), administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and AAMA.
MAJ Douglas R. Hogoboom, D.O. is a flight surgeon at the U.S. Army School of Aviation Medicine; Dr. Michael T. Acromite, MD, MSPH, FACOG, FASMA is a specialist in obstetrics & gynecology and aerospace medicine and a senior research fellow at the U.S. Army Aeromedical Activity. Both are located at Fort Rucker, AL.