Is it safe to fly during pregnancy?
http://www.100md.com
《中华医药杂志》英文版
1 Department of General Obstetrics & Gynecology,KK Womens and Childrens Hospital,100 Bukit Timah Road,229899,Singapore
2 Department of Ophthalmology,KK Womens and Childrens Hospital,100 Bukit Timah Road,229899,Singapore
Correspondence to Dr Pin Min LAM, Department of Ophthalmology, KK Womens and Childrens Hospital, 100 Bukit Timah Road, 229899,Singapore
Tel: (65) 63941157, Fax: (65) 62910161,E-mail: vpmlam@yahoo.com.sg
[Abstract] Objective The number of people travelling by commercial aircraft in recent years is unprecedented. Over the last 30 years, the number of air passenger worldwide has nearly quadrupled, from 383 million in 1970 to 1 462 million in 1998. The aviation environment is complex and potentially dangerous. There have been doubts about the safety of flying in pregnant mothers. To complicated matters, the advent of ultra-long range aircraft such as the Airbus 345 and Boeing 777LR, has made non-stop air travel up to a gruelling 18~19 hours a reality.Methods A review of existing literature is done using the PubMed search for “Flying in Pregnancy”.Results and Conclusion Air travel is generally safe and most major airlines in the world would allow unrestricted travel for pregnant passengers up to 35th or 36th week of singleton pregnancy and 32nd week for multiple (twin) pregnancy. Unless there are complications, pregnant women need take no special precautions when travelling by air. Air travel is not recommended for women who have medical or obstetric complications, such as pregnancy-induced hypertension, poorly controlled diabetes or sickle cell disease, that could result in an emergency, who are at significant risk for premature labour or who have placental abnormalities. Unless absolutely necessary, it is also recommended that travelling during the first trimester be deferred as there is a small risk of cosmic radiation effect on the developing fetus.
[Key words] fly;pregnancy;safe
INTRODUCTION
The number of people travelling by commercial aircraft in recent years is unprecedented. Over the last 30 years, the number of air passengers worldwide has nearly quadrupled, from 383 million in 1970 to 1 462 million in 1998. More older and younger people are flying, including pregnant mothers with or without medical problems, adults with medical conditions (e.g., cardiovascular and pulmonary disease), children, and infants. To complicated matters, the advent of ultra-long range aircraft such as the Airbus 345 and Boeing 777LR, has made non-stop air travel up to a gruelling 18~19 hours a reality.
THE CABIN ENVIRONMENT
The aircraft cabin is similar to other indoor environments, such as air-conditioned homes and offices, in that people are exposed to a mixture of outside and re-circulated air. However, the cabin environment is different in many respects-for example, the high occupant density, the inability of occupants to leave at will, and the need for cabin pressurisation. In flight, people encounter a combination of peculiar environmental factors that includes low humidity, reduced air pressure, changes in cabin pressures, noise, and potential exposure to air contaminants, such as ozone (O3), carbon monoxide (CO), various organic chemicals, and biological agents.
Low Cabin Atmospheric Pressure / Hypoxia
Subsonic commercial airliners normally cruise at altitudes of 30 000~33 000 feet. The outside atmospheric pressure at these cruising altitudes is extremely low, with a corresponding partial pressure of oxygen of only about 40 mm Hg. Such low level of oxygen tension can only sustain life for a few minutes, without supplemental oxygenation. For this reason the cabin of airliners are usually pressurised to an equivalent outside atmosphere of around 6 000~8 000 ft. At this cabin altitude, the partial pressure of oxygen drops from the sea-level value of 148 mm Hg to 108 mm Hg, equivalent to a fall of about 27%. Every passenger is essentially mildly hypoxic although certainly not symptomatic. Furthermore, even at this cabin altitude there is no serious effect on fetal oxygenation due to the fetal hemoglobin dissociation curve. However, certain passengers, particularly those suffering from cardio-respiratory diseases or severe anemia, may be unable to tolerate and can manifest hypoxic symptoms and adverse effects.
Changes in Cabin Pressurisation
The cabin atmospheric pressure changes[4] during ascent and descent. The maximum rate of increase in cabin pressure adopted for most commercial airliners is 1 kPa (0.15 lb/in2) / minute, that is, about 300 feet / minute. Gas expansion within the gastrointestinal tract, which expands because of reduction of environmental pressure, rarely gives rise to anything more than transient discomfort or flatulence. However, in patients with upper respiratory tract infection or the slightest blockage of sinuses or the eustachian tubes, air can be trapped in sinuses or the middle ear cavity resulting in sinus or otitic barotrauma respectively. In pregnancy both lymphatic and nasal congestion associated with fluid retention[3] have been reputed to cause just these effects.
Cosmic Radiation
Cosmic radiation[11,13,14] contributes about 13% of the natural background radiation level. It is believed to come from Milky Way galaxy but its origin is unclear. Cosmic radiation is the sum of galactic (from outer space) and solar (from the sun) radiation. It consists primarily of charged and neutral particles (protons, alpha particles, heavier ions, and electrons) and secondary particles generated by interaction of cosmic radiation with atmospheres air (ions, neutrons, gamma rays, electrons, etc).
Everybody is exposed to background radiation, be it natural from housing materials, soil, rocks, or medical from X-rays, etc., or cosmic from the universe. The earths atmosphere and magnetic field serve as a strong barrier against cosmic radiation and as such, only relatively small quantities reach the earths surface. Naturally, at high altitude the atmosphere is thinner, and so our exposure to radiation increases.
Short-haul flights are flown at lower altitudes than long-haul flights. Consequently, there is more radiation shielding provided by atmospheric air at lower altitudes and lower dose received from cosmic radiation. The latitude of the flight route also makes a difference in the level of cosmic radiation exposure. If two same-distance flights are flown at different geographic latitudes but at the same altitude, the cosmic radiation level on the lower-latitude flight will be usually lower of the two because of the greater shielding factor provided by earths magnetic field. This shielding is maximum at the equator and gradually decreases to zero at the south and north poles.
For the vast majority of air travellers these short periods at altitude do not represent a significantly long enough period exposed to cosmic radiation. The average traveller is therefore unlikely to fly regularly enough to experience any harmful effects from cosmic radiation. Frequent fliers and airline staff, however, can spend a large proportion of their time at altitude and thus have a longer exposure to radiation, which can be 100~300 times the level found at sea level.
The biological effect of radiation on the human body depends not only on its energy but also on its composition (alpha, gamma, proton, neutron, etc.), so that a weighting factor is applied to produce a meaningful unit of “harmful effect”, called the Sievert (Sv). This unit can be further subdivided into a thousand milli Sieverts (mSv), each of which in turn consist of one thousand microsieverts (μSv). These units can also be expressed per hour (h) or per year (y).
Annual exposure dose limit for a member of general public is 1 milli-Sieverts (mSv) and occupational limits is 5 mSv. Exposure dose from cosmic radiation at flight altitudes is usually not higher than 0.005 mSv per hour. Rough estimates show that it will take a minimum of 200 flight hours to approach annual dose limit for general public.
Noise
There is an excess of both low and high frequency noise[6] in most aircraft cabins. The smaller turbo-prop powered commuter planes are usually the worst. The uterus and amniotic fluid may accentuate low frequency sounds and only weakly attenuate high frequency sounds, perhaps by no more than 10 decibels (dB). The unborn child is more susceptible to hearing damage[9] than adults for a given sound pressure exposure. The effects of high decibel noise are unknown, but studies in Canada[7] link 3-fold increase in infant hearing loss to occupational noise exposure during pregnancy as low as 90 dB.
Low Humidity
The relative humidity in aircraft cabins is low, usually less than 20%. Low humidity may cause discomfort of the eyes, mouth, and nose but presents little risk to health. Maintaining good fluid intake before and during the flight can alleviate discomfort. Skin-moisturising lotion and a saline nasal spray can be used for the skin and nasal passages respectively.
Cabin Air Quality
Air within the cabin[4] is re-circulated (50%) to be mixed with air coming from the outside atmosphere (50%). Aircraft re-circulation systems exchange the air some 5~10 times more frequently than in buildings. High efficiency particulate air (HEPA) filters[6] ensure that contaminants such as microorganisms and smoke particles are removed. Without a humidifying system, low humidity is inevitable in aircraft operating at moderate and high altitudes.
The concentration of ozone (triatomic oxygen, O3) increases with altitude. The FAA limit is 0.1 parts per million by volume (ppmv) over any 3-hour period or 0.25 ppmv at any one time, whereas 0.8 ppmv has been measured at altitude on occasion.Ozone has also been shown to produce chromosomal damage and interact with damage caused by other agents, e.g. radiation. Ozone converters are not standard equipment on short haul aircraft. In modern jet aircraft, almost all ozone in the ambient air is converted to oxygen in the compressors that provide pressurised air for the cabin. During descent, when engine power is low, a build-up of ozone is prevented by catalytic converters.
POTENTIAL ISSUES WITH PREGNANT PASSENGERS
Pre-flight
There are two screening devices at the airport. One is an X-ray machine that screens the luggage and the other a metal-detecting device prior to boarding. The X-ray machine is well shielded and exposes no one to any significant exposure to X-rays neither the workers or the passengers. The other metal-detecting device utilises non-ionising electromagnetic “radiation.” Exposure to this has no reported adverse effects on the fetus or the reproductive system.
In-flight
General discomfort Pregnant passengers who are late in their pregnancy are very gravid and may experience discomfort in their seats, especially if travelling on economy class. Long-haul flights and inability of the seats to recline comfortably can aggravate backaches that may have already existed during pregnancy.
Spontaneous abortion (miscarriage) It is important to note that there is a background risk of birth defects (3%) and miscarriage (15%) in the first trimester. Studies on pregnant cabin crewmembers have suggested that there is a slightly increased risk of spontaneous abortion among female cabin crewmembers who continue to work during their early pregnancy. However, this result may not be extrapolated to pregnant passengers who do not travel as frequently during their early pregnancy.
Motion sickness The air turbulence in flying can result in motion sickness in susceptible individuals and exacerbate morning sickness in pregnant passenger, especially those in the first trimester. The smell from aircraft food can be nauseating to some passengers, and can make the flight rather unpleasant for susceptible.
Immobility and circulatory problems Prolonged immobility, particularly in ultra-long haul flight, when the individual is seated, leads to pooling of blood in the legs, which in turn causes swelling, stiffness, and discomfort. Circulatory stasis is a predisposing factor for the development of venous thrombosis (blood clots), also know as economy class syndrome. In the case of air travel, it is possible, but not scientifically proven, that other factors in the flight environment also contribute.
Most venous thrombi do not cause any symptoms and are reabsorbed without any consequences. Occasionally, if a thrombus detaches from the lining of the vein and travels in the bloodstream to the lungs (pulmonary embolism), deep-vein thrombosis[10~12] may have serious consequences including chest pain, shortness of breath, and even sudden death. This may occur many hours or even days after the formation of the thrombus. In general, the risk of developing deep-vein thrombosis is relatively small. However, this risk is increased in pregnant passengers because of the changes in the coagulation status.
Hypoxia The cabin altitude of about 8 000 causes a mild hypoxic[10~12] environment. Pregnant passengers who are anemic may suffer more significant hypoxic effects, though the fetus is usually spared because of the fetal hemoglobin dissociation curve. However, fetus of severely anemic mothers who are unaware of their condition, may suffer from fetal distress.
Barotrauma The changes in cabin pressures can cause expansion and contraction of trapped gases in the body, such as in the sinuses and middle ear cavity. In pregnancy both lymphatic and nasal congestion associated with fluid retention have been reputed to cause blockage of the eustachian tube and sinus openings. This can result in barotrauma if attempts to clear the ears and sinuses with medications fail.
Cosmic radiation Background cosmic radiation[13,14] levels are higher at altitude. Ionising radiation has been shown to result in cell damage, genetic mutation and cancer occurrence in the long term. Air travel should, therefore, be avoided, if possible, during the first three months of pregnancy as small amounts of radiation can potentially be harmful to the developing fetus.
Noise There is an excess of both low and high frequency noise in most aircraft cabins. The smaller turbo-prop powered commuter planes are usually the worst. The uterus and amniotic fluid may accentuate low frequency sounds and only weakly attenuate high frequency sounds, perhaps by no more than 10 decibels (dB). The fetus is more susceptible to hearing damage than adults for a given sound pressure exposure.
Emergency egress The mobility of pregnant passengers, especially those in third trimester and near term can be seriously impaired. This can hinder movement and egress of the aircraft during an emergency, affecting survivability.
Preterm labour The stress of travelling, both physical and emotional can result in preterm labour. The lack of medical expertise onboard and the uncertainties of the labour process (e.g. complications of labour) can have dire consequences to both the mother and the child.
Isolation from proper obstetric care One of the major risks faced by pregnant passengers is the lack of proper obstetric care when travelling in the aircraft. Unexpected obstetric or medical emergencies can happen and little medical attention can be offered in the aircraft.
EXISTING POLICIES[15] ON PREGNANT PASSENGERS FLYING ON SOME MAJOR AIRLINES
Aeroflot
A doctors certificate is required if travelling within four weeks of due date. The certificate must state that the passenger has been examined and must be dated within seven days of flight departure.
American Airlines
A doctors letter indicating safe for travel, signed within 48 hours of travel, is required if the passenger is travelling within 30 days of due date. If the travel is within ten days before or seven days after delivery date, a doctors letter plus clearance by AA Special Assistance Co-ordinator are required.
British Airways
For uncomplicated single pregnancies, British Airways restricts travel beyond the end of the 36th week, and for multiple pregnancies (twins, triplets etc.), beyond the end of the 32nd week. Passengers beyond the 28th week of gestation are required to carry a letter from the doctor or midwife, stating the pregnancy is uncomplicated and confirming the expected date of delivery. The doctor should also certify that the traveller is in good health and there is no reason to restrict flying.
British Midlands
British Midlands has no travel restrictions up to the 30th week of pregnancy. However, a doctors certification is required for pregnant travellers in their 30th to 36th week of pregnancy. Travel after the 36th week of pregnancy is not normally allowed.
Delta Airlines / Alaskan Airlines
Both Delta Airlines and Alaskan Airlines do not impose any form of restriction on pregnant passengers.
EasyJet
There is no restriction for pregnant passengers travelling up to the 27th week of pregnancy. A doctors certificate is, however, required if travelling between the 28th and 35th week of pregnancy. EasyJet does not accept medical certificates supplied by a registered midwife. No travel is permitted beyond the 36th week of pregnancy.
Singapore Airlines
For normal uncomplicated pregnancies, air travel is allowed up to 35th week of pregnancy, with certification from a doctor. Unrestricted air travel for twin pregnancies is allowed up to 32nd week of pregnancy, with certification from a doctor. Passengers with multiple (triplets or above) pregnancies will not be allowed to travel on the airline at any stage of the pregnancy. Pregnant passenger with medical problems will be allowed to travel, subject to Singapore Airlines doctors approval and recommendations. For urgent or compassionate cases, expectant mothers may be accepted for carriage after limiting dates, but only with consent from the Airlines doctors. However, they should be accompanied by a doctor or a nurse.
South African Airways
South African Airways advises against travel after the 34th week of pregnancy. Passengers who are beyond the 35th week of pregnancy will not be accepted for travel on international flights without a doctors certificate. Travel with a doctors certificate is also subject to the approval of South African Airways medical officials. Passengers who are beyond the 36th week of pregnancy will not be accepted for travel on domestic flights without a doctors certificate. Travel with a doctors certificate is also subject to the approval of South African Airways medical officials.
United Airlines
The United Airlines does not impose any restrictions on pregnant passengers during the first 8 months of pregnancy. For travelling during the 9th month, a doctors letter is required in triplicate, signed within 72 hours of travel, indicating due date and that the air travel does not pose a health risk to the passenger.
Valuair
Valuair allows unrestricted travel for normal pregnancy up to 35th week of pregnancy and twin pregnancy up to 32nd week of pregnancy. However, passenger must hold a certificate of fitness for air travel from the attending obstetrician. Pregnant travellers with medical problem may be allowed to travel, subject to Valuair doctors approval. Medical certificate from attending obstetrician is also required.
Virgin Atlantic
Travel is permitted without restrictions until the 28th week of pregnancy provided that the pregnancy is free from complications. Virgin Atlantic asks that their Special Assistance department be informed of pregnancy so that they can supply appropriate inflight health advice. Between the 28th and 34th weeks of pregnancy a doctors certificate is required. The certificate must state that the passenger is safe for travel and the expected due date. Beyond the 34th week of pregnancy, travel is only permitted for medical/compassionate reasons and the pregnant passenger is required to be accompanied by a nurse or doctor. This travel is subject to the approval of a Virgin Atlantic doctor.
CONCLUSION
Air travel is generally safe and most major airlines in the world would allow unrestricted travel for pregnant passengers up to 35th or 36th week of singleton pregnancy and 32nd week for multiple (twin) pregnancy. Unless there are complications, pregnant women need take no special precautions when travelling by air. Air travel is not recommended for women who have medical or obstetric complications, such as pregnancy-induced hypertension, poorly controlled diabetes or sickle cell disease, that could result in an emergency, who are at significant risk for premature labour or who have placental abnormalities. Unless absolutely necessary, it is also recommended that travelling during the first trimester be deferred as there is a small risk of cosmic radiation effect on the developing fetus.
REFERENCES
1. Aspholm R, Lindbohm ML, Paakkulainen H, Taskinen H, Nurminen T, Tiitinen A. Spontaneous abortions among Finnish flight attendants. J Occup Environ Med,1999,41(6):486-491.
2. Breathnach F, Geoghegan T, Daly S, Turner MJ. Air travel in pregnancy: the ‘air-born study. Ir Med J, 2004,97(6):167-168.
3. DeCherney AH, Pernoll ML.Current Obstetric & Gynecologic Diagnosis & Treatment,8th ed.America:Appleton Lange Med,1995.
4. Ernsting J, Nicholson AN, Rainford DJ.et al.Aviation Medicine, 3rd ed.Oxford:Butterworth Heinemann,1999.
5. Friedberg W, Faulkner DN, Snyder L, Darden EB Jr, OBrien K. Galactic cosmic radiation exposure and associated health risks for air carrier crewmembers. Aviat Space Environ Med, 1989,60(11):1104-1108.
6. Hunt EH, Space DR.The Airplane Cabin Environment,Issue pertaining to flight attendant comfort.The Boeing Company,International In-Flight service management organization conference,Montreal,Canada.
7. Lalande NM, Hetu R, Lambert J. Is occupational noise exposure during preganncy a risk factor of damage to the auditory system of the fetus?Am J. Ind Med,1986, 10(4): 427-435.
8. Newlands JC, Barclay JR. Air transport of passengers of advanced gestational age. Aviat Space Environ Med,2000,71(8):839-842.
9. Piewrson LL. Hazards of noise exposure on fetal hearing.Semin Perinatol, 1996,20(1): 21-29.
10. Rayman RB, Hastings JD, Kruyer WB, Levy RA.Clinical Aviation Medicine.Third Edition,279-281.
11. Rayman RB. Passenger safety, health and comfort: a review. Aviat Space Environ Med, 1997,68(5): 432-440.
12. Scholten P. Pregnant stewardess-should she fly? Aviat Space Environ Med, 1976,47(1):77-81.
13. Sigurdson AJ, Ron E. Cosmic radiation exposure and cancer risk among flight crew. Cancer Invest, 2004,22(5) : 743-761.
14. Wallace RW, Sondhaus CA. Cosmic radiation exposure in subsonic air transport. Aviat Space Environ Med,1978,49(4):610-623.
15. Websites of the different airlines. www.britishairways.com, www.aa.com, www.alaskaair.com, www.delta.com, www.united.com, www.singaporeair.com, www.thebritishmidlands.com, www.virgin-atlantic.com, www.valuair.com.sg, www.saa.co.za, www.easyjet.com
(Editor Jaque)(Jeanette Suet Ching CHEN1)
2 Department of Ophthalmology,KK Womens and Childrens Hospital,100 Bukit Timah Road,229899,Singapore
Correspondence to Dr Pin Min LAM, Department of Ophthalmology, KK Womens and Childrens Hospital, 100 Bukit Timah Road, 229899,Singapore
Tel: (65) 63941157, Fax: (65) 62910161,E-mail: vpmlam@yahoo.com.sg
[Abstract] Objective The number of people travelling by commercial aircraft in recent years is unprecedented. Over the last 30 years, the number of air passenger worldwide has nearly quadrupled, from 383 million in 1970 to 1 462 million in 1998. The aviation environment is complex and potentially dangerous. There have been doubts about the safety of flying in pregnant mothers. To complicated matters, the advent of ultra-long range aircraft such as the Airbus 345 and Boeing 777LR, has made non-stop air travel up to a gruelling 18~19 hours a reality.Methods A review of existing literature is done using the PubMed search for “Flying in Pregnancy”.Results and Conclusion Air travel is generally safe and most major airlines in the world would allow unrestricted travel for pregnant passengers up to 35th or 36th week of singleton pregnancy and 32nd week for multiple (twin) pregnancy. Unless there are complications, pregnant women need take no special precautions when travelling by air. Air travel is not recommended for women who have medical or obstetric complications, such as pregnancy-induced hypertension, poorly controlled diabetes or sickle cell disease, that could result in an emergency, who are at significant risk for premature labour or who have placental abnormalities. Unless absolutely necessary, it is also recommended that travelling during the first trimester be deferred as there is a small risk of cosmic radiation effect on the developing fetus.
[Key words] fly;pregnancy;safe
INTRODUCTION
The number of people travelling by commercial aircraft in recent years is unprecedented. Over the last 30 years, the number of air passengers worldwide has nearly quadrupled, from 383 million in 1970 to 1 462 million in 1998. More older and younger people are flying, including pregnant mothers with or without medical problems, adults with medical conditions (e.g., cardiovascular and pulmonary disease), children, and infants. To complicated matters, the advent of ultra-long range aircraft such as the Airbus 345 and Boeing 777LR, has made non-stop air travel up to a gruelling 18~19 hours a reality.
THE CABIN ENVIRONMENT
The aircraft cabin is similar to other indoor environments, such as air-conditioned homes and offices, in that people are exposed to a mixture of outside and re-circulated air. However, the cabin environment is different in many respects-for example, the high occupant density, the inability of occupants to leave at will, and the need for cabin pressurisation. In flight, people encounter a combination of peculiar environmental factors that includes low humidity, reduced air pressure, changes in cabin pressures, noise, and potential exposure to air contaminants, such as ozone (O3), carbon monoxide (CO), various organic chemicals, and biological agents.
Low Cabin Atmospheric Pressure / Hypoxia
Subsonic commercial airliners normally cruise at altitudes of 30 000~33 000 feet. The outside atmospheric pressure at these cruising altitudes is extremely low, with a corresponding partial pressure of oxygen of only about 40 mm Hg. Such low level of oxygen tension can only sustain life for a few minutes, without supplemental oxygenation. For this reason the cabin of airliners are usually pressurised to an equivalent outside atmosphere of around 6 000~8 000 ft. At this cabin altitude, the partial pressure of oxygen drops from the sea-level value of 148 mm Hg to 108 mm Hg, equivalent to a fall of about 27%. Every passenger is essentially mildly hypoxic although certainly not symptomatic. Furthermore, even at this cabin altitude there is no serious effect on fetal oxygenation due to the fetal hemoglobin dissociation curve. However, certain passengers, particularly those suffering from cardio-respiratory diseases or severe anemia, may be unable to tolerate and can manifest hypoxic symptoms and adverse effects.
Changes in Cabin Pressurisation
The cabin atmospheric pressure changes[4] during ascent and descent. The maximum rate of increase in cabin pressure adopted for most commercial airliners is 1 kPa (0.15 lb/in2) / minute, that is, about 300 feet / minute. Gas expansion within the gastrointestinal tract, which expands because of reduction of environmental pressure, rarely gives rise to anything more than transient discomfort or flatulence. However, in patients with upper respiratory tract infection or the slightest blockage of sinuses or the eustachian tubes, air can be trapped in sinuses or the middle ear cavity resulting in sinus or otitic barotrauma respectively. In pregnancy both lymphatic and nasal congestion associated with fluid retention[3] have been reputed to cause just these effects.
Cosmic Radiation
Cosmic radiation[11,13,14] contributes about 13% of the natural background radiation level. It is believed to come from Milky Way galaxy but its origin is unclear. Cosmic radiation is the sum of galactic (from outer space) and solar (from the sun) radiation. It consists primarily of charged and neutral particles (protons, alpha particles, heavier ions, and electrons) and secondary particles generated by interaction of cosmic radiation with atmospheres air (ions, neutrons, gamma rays, electrons, etc).
Everybody is exposed to background radiation, be it natural from housing materials, soil, rocks, or medical from X-rays, etc., or cosmic from the universe. The earths atmosphere and magnetic field serve as a strong barrier against cosmic radiation and as such, only relatively small quantities reach the earths surface. Naturally, at high altitude the atmosphere is thinner, and so our exposure to radiation increases.
Short-haul flights are flown at lower altitudes than long-haul flights. Consequently, there is more radiation shielding provided by atmospheric air at lower altitudes and lower dose received from cosmic radiation. The latitude of the flight route also makes a difference in the level of cosmic radiation exposure. If two same-distance flights are flown at different geographic latitudes but at the same altitude, the cosmic radiation level on the lower-latitude flight will be usually lower of the two because of the greater shielding factor provided by earths magnetic field. This shielding is maximum at the equator and gradually decreases to zero at the south and north poles.
For the vast majority of air travellers these short periods at altitude do not represent a significantly long enough period exposed to cosmic radiation. The average traveller is therefore unlikely to fly regularly enough to experience any harmful effects from cosmic radiation. Frequent fliers and airline staff, however, can spend a large proportion of their time at altitude and thus have a longer exposure to radiation, which can be 100~300 times the level found at sea level.
The biological effect of radiation on the human body depends not only on its energy but also on its composition (alpha, gamma, proton, neutron, etc.), so that a weighting factor is applied to produce a meaningful unit of “harmful effect”, called the Sievert (Sv). This unit can be further subdivided into a thousand milli Sieverts (mSv), each of which in turn consist of one thousand microsieverts (μSv). These units can also be expressed per hour (h) or per year (y).
Annual exposure dose limit for a member of general public is 1 milli-Sieverts (mSv) and occupational limits is 5 mSv. Exposure dose from cosmic radiation at flight altitudes is usually not higher than 0.005 mSv per hour. Rough estimates show that it will take a minimum of 200 flight hours to approach annual dose limit for general public.
Noise
There is an excess of both low and high frequency noise[6] in most aircraft cabins. The smaller turbo-prop powered commuter planes are usually the worst. The uterus and amniotic fluid may accentuate low frequency sounds and only weakly attenuate high frequency sounds, perhaps by no more than 10 decibels (dB). The unborn child is more susceptible to hearing damage[9] than adults for a given sound pressure exposure. The effects of high decibel noise are unknown, but studies in Canada[7] link 3-fold increase in infant hearing loss to occupational noise exposure during pregnancy as low as 90 dB.
Low Humidity
The relative humidity in aircraft cabins is low, usually less than 20%. Low humidity may cause discomfort of the eyes, mouth, and nose but presents little risk to health. Maintaining good fluid intake before and during the flight can alleviate discomfort. Skin-moisturising lotion and a saline nasal spray can be used for the skin and nasal passages respectively.
Cabin Air Quality
Air within the cabin[4] is re-circulated (50%) to be mixed with air coming from the outside atmosphere (50%). Aircraft re-circulation systems exchange the air some 5~10 times more frequently than in buildings. High efficiency particulate air (HEPA) filters[6] ensure that contaminants such as microorganisms and smoke particles are removed. Without a humidifying system, low humidity is inevitable in aircraft operating at moderate and high altitudes.
The concentration of ozone (triatomic oxygen, O3) increases with altitude. The FAA limit is 0.1 parts per million by volume (ppmv) over any 3-hour period or 0.25 ppmv at any one time, whereas 0.8 ppmv has been measured at altitude on occasion.Ozone has also been shown to produce chromosomal damage and interact with damage caused by other agents, e.g. radiation. Ozone converters are not standard equipment on short haul aircraft. In modern jet aircraft, almost all ozone in the ambient air is converted to oxygen in the compressors that provide pressurised air for the cabin. During descent, when engine power is low, a build-up of ozone is prevented by catalytic converters.
POTENTIAL ISSUES WITH PREGNANT PASSENGERS
Pre-flight
There are two screening devices at the airport. One is an X-ray machine that screens the luggage and the other a metal-detecting device prior to boarding. The X-ray machine is well shielded and exposes no one to any significant exposure to X-rays neither the workers or the passengers. The other metal-detecting device utilises non-ionising electromagnetic “radiation.” Exposure to this has no reported adverse effects on the fetus or the reproductive system.
In-flight
General discomfort Pregnant passengers who are late in their pregnancy are very gravid and may experience discomfort in their seats, especially if travelling on economy class. Long-haul flights and inability of the seats to recline comfortably can aggravate backaches that may have already existed during pregnancy.
Spontaneous abortion (miscarriage) It is important to note that there is a background risk of birth defects (3%) and miscarriage (15%) in the first trimester. Studies on pregnant cabin crewmembers have suggested that there is a slightly increased risk of spontaneous abortion among female cabin crewmembers who continue to work during their early pregnancy. However, this result may not be extrapolated to pregnant passengers who do not travel as frequently during their early pregnancy.
Motion sickness The air turbulence in flying can result in motion sickness in susceptible individuals and exacerbate morning sickness in pregnant passenger, especially those in the first trimester. The smell from aircraft food can be nauseating to some passengers, and can make the flight rather unpleasant for susceptible.
Immobility and circulatory problems Prolonged immobility, particularly in ultra-long haul flight, when the individual is seated, leads to pooling of blood in the legs, which in turn causes swelling, stiffness, and discomfort. Circulatory stasis is a predisposing factor for the development of venous thrombosis (blood clots), also know as economy class syndrome. In the case of air travel, it is possible, but not scientifically proven, that other factors in the flight environment also contribute.
Most venous thrombi do not cause any symptoms and are reabsorbed without any consequences. Occasionally, if a thrombus detaches from the lining of the vein and travels in the bloodstream to the lungs (pulmonary embolism), deep-vein thrombosis[10~12] may have serious consequences including chest pain, shortness of breath, and even sudden death. This may occur many hours or even days after the formation of the thrombus. In general, the risk of developing deep-vein thrombosis is relatively small. However, this risk is increased in pregnant passengers because of the changes in the coagulation status.
Hypoxia The cabin altitude of about 8 000 causes a mild hypoxic[10~12] environment. Pregnant passengers who are anemic may suffer more significant hypoxic effects, though the fetus is usually spared because of the fetal hemoglobin dissociation curve. However, fetus of severely anemic mothers who are unaware of their condition, may suffer from fetal distress.
Barotrauma The changes in cabin pressures can cause expansion and contraction of trapped gases in the body, such as in the sinuses and middle ear cavity. In pregnancy both lymphatic and nasal congestion associated with fluid retention have been reputed to cause blockage of the eustachian tube and sinus openings. This can result in barotrauma if attempts to clear the ears and sinuses with medications fail.
Cosmic radiation Background cosmic radiation[13,14] levels are higher at altitude. Ionising radiation has been shown to result in cell damage, genetic mutation and cancer occurrence in the long term. Air travel should, therefore, be avoided, if possible, during the first three months of pregnancy as small amounts of radiation can potentially be harmful to the developing fetus.
Noise There is an excess of both low and high frequency noise in most aircraft cabins. The smaller turbo-prop powered commuter planes are usually the worst. The uterus and amniotic fluid may accentuate low frequency sounds and only weakly attenuate high frequency sounds, perhaps by no more than 10 decibels (dB). The fetus is more susceptible to hearing damage than adults for a given sound pressure exposure.
Emergency egress The mobility of pregnant passengers, especially those in third trimester and near term can be seriously impaired. This can hinder movement and egress of the aircraft during an emergency, affecting survivability.
Preterm labour The stress of travelling, both physical and emotional can result in preterm labour. The lack of medical expertise onboard and the uncertainties of the labour process (e.g. complications of labour) can have dire consequences to both the mother and the child.
Isolation from proper obstetric care One of the major risks faced by pregnant passengers is the lack of proper obstetric care when travelling in the aircraft. Unexpected obstetric or medical emergencies can happen and little medical attention can be offered in the aircraft.
EXISTING POLICIES[15] ON PREGNANT PASSENGERS FLYING ON SOME MAJOR AIRLINES
Aeroflot
A doctors certificate is required if travelling within four weeks of due date. The certificate must state that the passenger has been examined and must be dated within seven days of flight departure.
American Airlines
A doctors letter indicating safe for travel, signed within 48 hours of travel, is required if the passenger is travelling within 30 days of due date. If the travel is within ten days before or seven days after delivery date, a doctors letter plus clearance by AA Special Assistance Co-ordinator are required.
British Airways
For uncomplicated single pregnancies, British Airways restricts travel beyond the end of the 36th week, and for multiple pregnancies (twins, triplets etc.), beyond the end of the 32nd week. Passengers beyond the 28th week of gestation are required to carry a letter from the doctor or midwife, stating the pregnancy is uncomplicated and confirming the expected date of delivery. The doctor should also certify that the traveller is in good health and there is no reason to restrict flying.
British Midlands
British Midlands has no travel restrictions up to the 30th week of pregnancy. However, a doctors certification is required for pregnant travellers in their 30th to 36th week of pregnancy. Travel after the 36th week of pregnancy is not normally allowed.
Delta Airlines / Alaskan Airlines
Both Delta Airlines and Alaskan Airlines do not impose any form of restriction on pregnant passengers.
EasyJet
There is no restriction for pregnant passengers travelling up to the 27th week of pregnancy. A doctors certificate is, however, required if travelling between the 28th and 35th week of pregnancy. EasyJet does not accept medical certificates supplied by a registered midwife. No travel is permitted beyond the 36th week of pregnancy.
Singapore Airlines
For normal uncomplicated pregnancies, air travel is allowed up to 35th week of pregnancy, with certification from a doctor. Unrestricted air travel for twin pregnancies is allowed up to 32nd week of pregnancy, with certification from a doctor. Passengers with multiple (triplets or above) pregnancies will not be allowed to travel on the airline at any stage of the pregnancy. Pregnant passenger with medical problems will be allowed to travel, subject to Singapore Airlines doctors approval and recommendations. For urgent or compassionate cases, expectant mothers may be accepted for carriage after limiting dates, but only with consent from the Airlines doctors. However, they should be accompanied by a doctor or a nurse.
South African Airways
South African Airways advises against travel after the 34th week of pregnancy. Passengers who are beyond the 35th week of pregnancy will not be accepted for travel on international flights without a doctors certificate. Travel with a doctors certificate is also subject to the approval of South African Airways medical officials. Passengers who are beyond the 36th week of pregnancy will not be accepted for travel on domestic flights without a doctors certificate. Travel with a doctors certificate is also subject to the approval of South African Airways medical officials.
United Airlines
The United Airlines does not impose any restrictions on pregnant passengers during the first 8 months of pregnancy. For travelling during the 9th month, a doctors letter is required in triplicate, signed within 72 hours of travel, indicating due date and that the air travel does not pose a health risk to the passenger.
Valuair
Valuair allows unrestricted travel for normal pregnancy up to 35th week of pregnancy and twin pregnancy up to 32nd week of pregnancy. However, passenger must hold a certificate of fitness for air travel from the attending obstetrician. Pregnant travellers with medical problem may be allowed to travel, subject to Valuair doctors approval. Medical certificate from attending obstetrician is also required.
Virgin Atlantic
Travel is permitted without restrictions until the 28th week of pregnancy provided that the pregnancy is free from complications. Virgin Atlantic asks that their Special Assistance department be informed of pregnancy so that they can supply appropriate inflight health advice. Between the 28th and 34th weeks of pregnancy a doctors certificate is required. The certificate must state that the passenger is safe for travel and the expected due date. Beyond the 34th week of pregnancy, travel is only permitted for medical/compassionate reasons and the pregnant passenger is required to be accompanied by a nurse or doctor. This travel is subject to the approval of a Virgin Atlantic doctor.
CONCLUSION
Air travel is generally safe and most major airlines in the world would allow unrestricted travel for pregnant passengers up to 35th or 36th week of singleton pregnancy and 32nd week for multiple (twin) pregnancy. Unless there are complications, pregnant women need take no special precautions when travelling by air. Air travel is not recommended for women who have medical or obstetric complications, such as pregnancy-induced hypertension, poorly controlled diabetes or sickle cell disease, that could result in an emergency, who are at significant risk for premature labour or who have placental abnormalities. Unless absolutely necessary, it is also recommended that travelling during the first trimester be deferred as there is a small risk of cosmic radiation effect on the developing fetus.
REFERENCES
1. Aspholm R, Lindbohm ML, Paakkulainen H, Taskinen H, Nurminen T, Tiitinen A. Spontaneous abortions among Finnish flight attendants. J Occup Environ Med,1999,41(6):486-491.
2. Breathnach F, Geoghegan T, Daly S, Turner MJ. Air travel in pregnancy: the ‘air-born study. Ir Med J, 2004,97(6):167-168.
3. DeCherney AH, Pernoll ML.Current Obstetric & Gynecologic Diagnosis & Treatment,8th ed.America:Appleton Lange Med,1995.
4. Ernsting J, Nicholson AN, Rainford DJ.et al.Aviation Medicine, 3rd ed.Oxford:Butterworth Heinemann,1999.
5. Friedberg W, Faulkner DN, Snyder L, Darden EB Jr, OBrien K. Galactic cosmic radiation exposure and associated health risks for air carrier crewmembers. Aviat Space Environ Med, 1989,60(11):1104-1108.
6. Hunt EH, Space DR.The Airplane Cabin Environment,Issue pertaining to flight attendant comfort.The Boeing Company,International In-Flight service management organization conference,Montreal,Canada.
7. Lalande NM, Hetu R, Lambert J. Is occupational noise exposure during preganncy a risk factor of damage to the auditory system of the fetus?Am J. Ind Med,1986, 10(4): 427-435.
8. Newlands JC, Barclay JR. Air transport of passengers of advanced gestational age. Aviat Space Environ Med,2000,71(8):839-842.
9. Piewrson LL. Hazards of noise exposure on fetal hearing.Semin Perinatol, 1996,20(1): 21-29.
10. Rayman RB, Hastings JD, Kruyer WB, Levy RA.Clinical Aviation Medicine.Third Edition,279-281.
11. Rayman RB. Passenger safety, health and comfort: a review. Aviat Space Environ Med, 1997,68(5): 432-440.
12. Scholten P. Pregnant stewardess-should she fly? Aviat Space Environ Med, 1976,47(1):77-81.
13. Sigurdson AJ, Ron E. Cosmic radiation exposure and cancer risk among flight crew. Cancer Invest, 2004,22(5) : 743-761.
14. Wallace RW, Sondhaus CA. Cosmic radiation exposure in subsonic air transport. Aviat Space Environ Med,1978,49(4):610-623.
15. Websites of the different airlines. www.britishairways.com, www.aa.com, www.alaskaair.com, www.delta.com, www.united.com, www.singaporeair.com, www.thebritishmidlands.com, www.virgin-atlantic.com, www.valuair.com.sg, www.saa.co.za, www.easyjet.com
(Editor Jaque)(Jeanette Suet Ching CHEN1)