Because of the favorable properties of fetal
hemoglobin (HbF), including increased oxygen carry
ing potential plus increased fetal hematocrit and the
Bohr effect, fetal PaO2 changes very little.
Huch studied the fetal physiologic changes inflight
at 3238 gestational wk.
Even though maternal cardiovascular changes were
noted, there were no differences in fetal beattobeat
variability, bradycardia, or tachycardia (44).
The commercial aircraft environment is not
generally considered hazardous to the normal pregna
ncy and is a much safer and more comfortable mode
of transportation during pregnancy when compared t
o most alternatives (6,7,12,20).
At a cabin altitude of 5000–8000 ft (1524–2438 m), the maternal hemoglobin remains 90% saturated even though PaO2 decreases to 64 mm Hg (55).
Also, there is no evidence that chronic
exposure in either commercial aircraft or livin
g at 10,170 ft (3100 m) causes significant pre
gnancyrelated
problems, and some air carrier
s allow pregnant flight attendants and pilots to
fly through the first two trimesters (13,15,22).
In the event of sudden decompression, all p
assengers should use supplemental oxygen.
Emergency descent procedures should negate
the risk for fetal evolved gas disorder that is p
ossible following prolonged decompression (4
6,56,63).
Difficulty in equalizing pressure in the middle ear
and sinus cavities most often occurs during descent f
rom altitude.
Hyperplasia of tissue in the nasal cavity and pharynx
during pregnancy may accentuate this problem.
Intestinal gas expansion at altitude could cause
additional discomfort in late pregnancy due to abdo
minal crowding (11).
For this reason, it is prudent to avoid gasproducing
foods in the days before a scheduled flight.
One study associated preterm rupture of membranes with reduced barometric pressure, but there are no data to associate either premature rupture of membranes or premature labor with commercial flight parameters.
There has been a single reported case of placental abruption during flight, but because abruption is not
a rare event, this single event may well have been coincidental
Because air travel can cause motion sickness, the practitioner should advise the pregnant traveler that the nausea and vomiting that occasionally occur in early pregnancy may be increased during flight (12).
Antiemetic medication should be considered for individuals who are already experiencing difficulties.
In addition, aircraft often encounter turbulent air, sometimes unexpectedly.
Even relatively minor trauma to the abdomen in the third trimester of pregnancy may be associated with placental abruption.
Pregnant travelers should be instructed to use their seat belts continuously while seated.
The lap belt should be worn snugly over the pelvis or upper thighs, thus reducing the potential for injury of abdominal contents.
Inflight ambulation in the cabin late in pregnancy should be done with caution due to changing center of gravity and abdominal prominence.
Pregnancy significantly increases this risk due to obstruction of the vena cava from uterine compression, dependent lower extremities, and altered clotting factors.
Therefore, it is particularly vital that pregnant flyers ambulate every hour or two.
Constricting garments are to be avoided; however, support stockings and comfortable supportive shoes would be helpful.
It may also be beneficial to request an aisle seat for easier ingress, egress, and periodic leg stretching.
Those late in pregnancy should avoid the seat adjacent to the emergency exits.
Pregnant women with prior venous thromboembolism phenomenon or medical condition s that predispose them to venous thrombosis need to discuss anticoagulant therapy with their physician.
Even though national aviation authorities may have no official policy regarding pregnant pilots or passen gers, many airline medical departments allow passen gers to fly at their discretion up to 36 wk gestational age.
Beyond 36 wk, medical certification by an obstetrician may be required, particularly for long haul, overwater flights.