Does air travel affect pregnancy outcome?
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- Freeman, M., Ghidini, A., Spong, C.Y. et al. Arch Gynecol Obstet (2004) 269: 274. doi:10.1007/s00404-003-0579-5
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To evaluate if air travel affects pregnancy outcome, all women with singleton, non anomalous fetuses, admitted for delivery at a gestational age >20.0 weeks over a 6-month period were asked if they traveled by airflight during pregnancy, including details of the destination and length of their flights and any complications during the travel. Pregnancy outcome was obtained by chart review. Statistical analysis included Student’s t-test, Mann-Whitney U test, chi square, Fisher’s exact test where appropriate, and linear and logistic regression analysis, with p<0.05 considered significant.
Two hundred twenty-two women were studied. Of these, 53% (n=118) traveled at least once during pregnancy (median 2 flights, range 1–12). The first flight was taken at a mean ± standard deviation gestational age of 13.3±7.6 weeks with average flight lasting 4±2 h. There were no differences in gestational age at delivery (39.1 vs. 38.4 weeks, p=0.07), neonatal birthweight (3,379 vs. 3,273 g, p=0.24), or rates of vaginal bleeding (2% vs. 5%, p=0.26), preterm delivery <37 weeks (9% vs. 14%, p=0.29), preeclampsia (5% vs. 6%, p=0.76), neonatal intensive care unit admission (13% vs. 16%, p=0.56), or cumulative adverse obstetric outcome (p=0.61) between those who did and did not air travel during pregnancy. Power analysis demonstrated that a sample size of 2,803 women in each group would be necessary to show that air travel has a protective effect against adverse pregnancy outcome (alpha = 0.05, beta = 0.80). There were no thromboembolic events complicating any of the pregnancies.
Our findings suggest that air travel is not associated with increased risk of complications for pregnancies that reach 20 weeks’ gestation.
KeywordsAir travel Pregnancy Pregnancy complications Anemia
There is a paucity of information regarding risks of air travel in pregnancy, most of it stemming from fairly old series that have reached contradictory conclusions. Whereas one study deduced that “such low level of hypoxia as that which exists in an aircraft has no possible effect on the foetus” , another author argued that the “changing mechanics of pregnancy lend credence to the argument that pregnant stewardesses should not fly” . Authors who studied the physiologic changes in pregnant women during jet air travel found that transcutaneous PO2 decreased during flight by as much as 25%, whereas PCO2 levels remained constant . Fetal heart rate significantly increased during takeoff and landing, however the baseline remained within the range of normal at all times. These findings suggest no hazards of flight for uncomplicated pregnancies. However, it has been argued that fetuses with decreased reserves, such as those growth restricted, may become compromised even for transient hypoxemia . Moreover, prolonged or repeated exposure to pressurized high altitude theoretically could impair fetal growth.
No epidemiological studies have been conducted so far to verify these hypothetical effects of air flight on pregnancy. The purpose of the present cohort study is to assess whether air travel during pregnancy affects outcome and if so, whether there is a differential effect of airflight at different gestational ages.
Materials and methods
Gestational age of 20 weeks or greater, because gestations at <20 weeks are not routinely admitted to Labor and Delivery
Singleton gestation, because multiple pregnancies are at increased risk for obstetric complications independently of air travel
Labor in the second stage, in order to exclude women with threatened preterm delivery
Excluded were fetal or neonatal structural or chromosomal anomalies (n=3), because the anomalies could account for adverse obstetric and neonatal outcome independently of air travel.
Medical history, obstetric complications and pregnancy outcome information was obtained by chart review by an investigator who was blinded to flying status. The following variables were collected: maternal age and race, parity, history of adverse pregnancy outcome, presence of pre-pregnancy complications (renal, cardiovascular, pulmonary, or autoimmune), medications during pregnancy, initial hematocrit at first prenatal visit and hematocrit at the time of delivery. Outcome variables analyzed were occurrence of pregnancy complications, perinatal mortality, gestational age at delivery, birth weight, birth weight centile, and admission to neonatal intensive care unit. The study was approved by the Institutional Review Board.
For statistical analysis, variables of interest were compared between women who admitted to air travel during pregnancy and those who did not using Mann-Whitney test, Chi-square and Fisher’s exact test, where appropriate. To assess whether longer flights have a heavier statistical impact than shorter flights, and whether the time of gestation when flight occurs impacts the outcome, we also created a weighted average gestational age at flight (duration of 1st flight * gestational age + duration 2nd flight * gestational age, etc./total hours airborne). To assess whether the time of gestation when flight occurs impacts the outcome, a variable of cumulative hours airborne by all patients at each trimester of pregnancy was calculated. A composite adverse pregnancy outcome variable was also used to increase the power to detect a significant adverse effect of air traveling. The composite variable consisted of the summation of stillbirth, 5-min Apgar score <7, delivery at <37 weeks, preeclampsia, and birth weight <10th centile. Linear and logistic regression analyses were used to control for confounding variables. A two-tailed p<0.05 or an odds ratio with 95% confidence interval not inclusive of the unity was considered statistically significant.
Demographic characteristics in relation to air travel during pregnancy. Mean ± SD or number (%)
Air travel yes (n=118)
Air travel no (n=104)
Maternal age (years)
Other medical problemsa
Pregnancy complications in relation to air travel during pregnancy Mean ± SD or number (%)
Air travel yes (n=118)
Air travel no (n=104)
Preterm labor requiring tocolysis
Initial hematocrit (%)
Gestational age at initial hematocrit (weeks)
Hematocrit at delivery (%)
Pregnancy outcome in relation to air travel during pregnancy. Mean ± SD or number (%). BP blood pressure, NICU neonatal intensive care unit
Air travel yes (n=118)
Air travel no (n=104)
Gestational age at delivery (weeks)
Preterm delivery <37 weeks
Mean BP at delivery (mm Hg)
Birth weight (grams)
Birth weight centile
Birth weight <10th centile
5-min Apgar <7 among live births
Admission to NICU
Adverse pregnancy outcome
Air travel during pregnancy does not seem to pose a significant risk to the pregnancy. The lack of an association between air traveling and any individual or composite adverse pregnancy outcome variable is a reassuring finding, as is the lack of any correlation between hours spent traveling or gestational age at air traveling and adverse outcome. Although our cohort may seem to be small, nearly half of the enrolled women did fly during pregnancy and the range of hours spent flying was large enough to allow meaningful statistical analysis. Our negative findings do not seem to be due to lack of power, as the trend is against the hypothesis that air travel causes adverse outcome. In other words air traveling was associated with a non-significant trend towards a lower rate of adverse pregnancy outcome. Our results provide support to the current ACOG recommendations that pregnant women can safely fly up to 36 weeks of gestation .
A potential confounding variable present in the study is the significant racial difference in women who did and did not travel. The higher rate of Caucasian women who traveled may reflect a sociodemographic difference between the two groups and it may also explain the higher hematocrit in the patients who traveled, as well as skew the pregnancy outcome results. Information regarding educational and economic status of recruited subjects was not obtained in our study. However, when we performed logistic regression analysis taking into account maternal race, as well as other demographic variables, there was no change in the lack of a significant association between air travel and composite adverse pregnancy outcome.
One may argue that those patients who did not travel were instructed to do so by their physician, thus preselecting a healthier population in the group that traveled. This bias is unlikely to be present in our study since the conditions that are likely to be considered as “contraindications” to flying (e.g., preterm labor requiring tocolysis or vaginal bleeding) were similarly represented in the two groups. Recall bias is another potential problem in our type of study. However, women admitted in preterm labor or experiencing pregnancy complications are generally expected to manifest a over-recall rather than an under-recall of potential causative factors. A limitation of our study is that by its design we were unable to evaluate whether air travel influences miscarriage rates. Indeed, a recent study detected a 30% increased risk of spontaneous abortion among flight attendants who worked during early pregnancy compared with those who did not . Only a cohort study with longitudinal follow-up of women throughout pregnancy and including travel patterns, medical complications, and medical advice, can address these potential biases and provide final answers to these questions. Although there were no cases of thromboembolism in our study population, our sample size was obviously underpowered to detect any effect of air travel on rates of deep vein thrombosis or pulmonary embolism.
In summary, the obstetrical complications typically cautioned about by medical practitioners, such as preterm labor or vaginal bleeding, were not increased in a cohort of women who traveled by airplane during pregnancy. Caution should be exercised before extrapolating our results to flight attendants or other personnel who spend much of their working hours flying. Future studies confirming these findings will improve physicians’ ability to counsel patients on the safety of air travel in pregnancy.