DR. DANIEL L.JOHNSON

The Pregnant Pilot -Only a woman can be a mom

I paraphrase a recent letter to preserveanonymity:

Dear Dr. Dan,I'm a glider pilot, and I'm pregnant. I

love soaring, and I was hoping to fly untilI could either no longer fit in the glideror could no longer comfortably reach thecontrols, but I don't want to cause harmto my fetus, our baby. My obstetriciansuggested that I stop soaring since shedoes not know what the changes in alti-tude will do to the fetus. I can't find anyreliable information on the risks of flyingin pregnancy.

What's safe?

The Simple Answer1 The main concern is hypoxia of the

fetus. Staying below 5000 ft msl (forlowland fliers) is clearly safe. At higheraltitudes, using oxygen as required byFederal Aviation Regulations is probablysafe.

2 The risks are generally small. Ob-stetrical emergencies are always a prob-lem when Mom has wandered off, awayfrom civilization. Being at altitude in aglider might feel remote from "civiliza-tion," if defined as "that part of the worldinhabited by a skilled equipped obstetri-cian" unless your alternate landing field isthe back lot of your local birthing center.

3 During the last trimester there arediscomforts and inconveniences withpregnancy that may make getting into asmall cockpit seem about as much fun astaking a long trip in the back seat of asubcompact car.

Explanations

Prudent Pregnant PilotingObviously, there are two risks in pilot-

ing an aircraft while pregnant. One is

that your abdominal size might restrictfull control movement or create distract-ing discomfort. The other is that thefetus, which lives in a low-oxygen envi-ronment in the uterus, might be harmedat altitude.

The issue of size is your responsibility,and the preflight control check will giveyou the answer every time. The questionof discomfort will be answered, shouldthere be any doubt, by climbing in andclipping on the seat belts.

A woman of normal weight, in thesemi-recumbent posture most glidersuse, will never find her abdomen actuallyprevents full back stick. Generally, andI've had much experience taking care ofmassively obese patients, a big belly be-gins to spill down the thighs, where itwould get in the way of a control stick,somewhere in the neighborhood of 100pounds over ideal body weight. At thispoint, the pilot is likely to be over grossin every single-seater on the planet.

Airplanes with control wheels are dif-ferent. For example, the 300-pound manwho owns a Cessna 152; I know of onesuch, and I did ask him, "Are you ableto get full up-elevator?" He changed thesubject quickly, and I don't plan to driveto his field to watch his preflight controlcheck.

Nevertheless, pregnancy is a normalhuman condition. Without obesity, thesize of the pregnant stomach makesa woman feel cumbersome, and putsmore gravity in the center; yet the chaiselounge position of modern gliders seemsdesigned for best comfort and function.When the gravid womb gets great, yourinsides get crowded aside and might bevery uncomfortable. The size at term de-pends on how much fluid is in the womb,how many fetuses are roommates, andtheir position.

There are gliders with side sticks (e.g.,HP-18 and Diana 2), and this might be-come interesting as your baby matureswithin you, while your innie becomesa vast outie. One that wiggles and gig-gles and tumbles and tiggles inside yourtummy. This is not, of course, a hazard toflight except for distraction. In any case,since your child's arms and hands are forabout 40 weeks bound tightly withinyour skin; you don't have to worry aboutit grabbing the stick. But of course, to doa loop, or to land safely, you may need fullback stick for a moment. So your pre-flight check should include making sure,as usual, that control movements are fulland free right up to that 40th week.

What about oxygen?After finding no specific research, I

wrote to Dr. John B. West, a revered ex-pert on altitude physiology, and asked,"I am wondering if you know of anyresearch specifically assessing fetal respi-ratory physiology in short-term exposureto altitude such as occurs with flying un-pressurized aircraft."

He said, "This is the kind of questionwhere there is really almost no evidenceto help us give an accurate reply." So wehave to consider indirect evidence, anduse our brains.

Obviously, if Mom never steps intoa glider, there's no risk. However, that'smindless and uninteresting. We all knowthat there are two opposite human ap-proaches to ignorance: (1) If you don'tnow it's safe, don't do it; and (2) Whatyou don't know can't hurt you. Choice (1)is really paralysis, choice (2) is foolish.

So let's be reasonable and lay out whatwe know, then let this expand our safeoptions.

The Fetus is Well EngineeredFundamentally, we run on oxygen

and fuel. Oxygen is carried through-out our body, through the blood, byred cells, packages of hemoglobin.Hemoglobin is a tangle of protein sur-rounding a molecule of iron. Hemoglo-bin comes in different flavors, each ofwhich adsorbs and releases oxygen atslightly different levels.

Different animal species have differenthemoglobins, each suited to the range ofoxygen levels in which it lives. Hemo-globin vacuums up oxygen at the higher

levels (higher partial pressures) of itsenvironment and releases it at the lowerlevels (partial pressures) of its tissues.

Mom's hemoglobin absorbs oxygenwell in her lungs and releases it well inher tissues. Her fetus, functionally, is atissue - so its hemoglobin must vacuumup oxygen at the same level (partial pres-sure) at which Mom's hemoglobin is re-leasing it.

Conveniently, fetal hemoglobin hasdifferent affinity for oxygen than adulthemoglobin, such that it does exactlythis. After birth, fetal hemoglobin gradu-ally disappears over the first few monthsand is replaced by adult hemoglobin.

Interestingly, there's a third type ofhuman hemoglobin, embryonic hemo-globin, that operates at an even loweroxygen level than fetal hemoglobin.This is present from the beginning ofgestation, before the blood circulationthrough the placenta has developed. Thisdisappears during the first trimester.

There are really three stages of low-oxygen risk for the fetus. The first occursearly, before a woman might even knowshe's pregnant, before the placenta hasdeveloped. Maternal hypoxia duringthis time would cause miscarriage, andI know of no research into the effects ofacute hypoxia on fetal loss.

The second stage is most of the preg-nancy, after the placenta and its circula-tion are well developed. Various abnor-malities and diseases can injure the fetusor cause its loss. There is research onboth animals and humans on long visitsto or moving to high altitude, but littleon short ascents that might cause acutehypoxia. Studies in sheep have shownthat blood supply to the uterus increasesduring ascent at 1000 ft/min, and up to15,000 ft msl the drop in fetal oxygenpartial pressure is only about 20% withno evidence of distress or injury. Preg-nant women have been monitored whileriding airliners, and cabin pressures of8500 to 11,500 ft msl have not causedany evidence of fetal distress.

The third stage is when the pregnancyis "at term," when the oxygen-transportcapacity of the placenta is near its maxi-mum. Many physiologic things can gosubtly and undetectably awry at thispoint, and at this point we tend to beanxious and skittish about taking anyrisks. For example, if there's a twin preg-

nancy, there's increased demand on theplacenta and energy supply, and all risksare greater.

Adjustment versus AdaptationAdaptation is a long-term response;

adjustment is a short-term response.For example, in Peru and in Tibet, na-tive populations have evolved adapta-tions to living at high altitude - 5,000meters / 15,000 feet, and both mothers

and babies do well. Mothers who havemoved to high altitude and lived therefor months or years have adapted physi-ologically, but even after years of adapta-tion their infants'birth weights are lowerand their complications more frequentthan native moms.

Visitors to high-altitude regions havemore trouble. Birth weights of infantsdecrease by about 100 grams per 1000meters of altitude. Researchers report

that lowland women visiting Coloradohave more premature births and moreobstetrical bleeding than those who livethere. Colorado is not Tibet, only about3000 meters (5000-7000 ft).

Adjustment comprises all the thingswe might provide a woman to decreasethe risk of altitude. In flying, "adjust-ment" means "use oxygen."

What Altitude for Oxygen?To be reasonable about oxygen use by

pregnant pilots, we can look at other evi-dence. One clue is the common experi-ence of pilots wherein putting on oxygenabove about 5000 ft msl at night makesthe lights brighter and more colorful.

This occurs because the retina is oneof the most oxygen-hungry tissues inthe body. The information is availablebecause we're always conscious of ourvision. A scientific study is well andgood, and can yield very specific knowl-edge, but there's nothing so convincingas personal experience.

So I'd recommend that pregnant pilotsturn on the oxygen at 5000 ft. after set-ting yourself up on the ground to avoidfussing around with switches and valveswhile flying.

How high should you go? I don't know.However, if you want to go reasonablyhigh, do purchase a pulse oximeter, learnhow to use it, and use it. (Oximeters werecovered in this column in June 2012. Ifyou don't have the magazine handy, go tohttp://www.danlj.org/~danlj/Soaring/SoaringRx/ to find it. May and Decem-ber 2011 and January 2012 also coveraspects of oxygen need and use.)

The safest thing, I think, is simply tocheck your saturation on the ground,and keep it within about 3% of this valuewhile flying, by adjusting the flow rate.

Flight LevelsOf course, it's possible to go into the

flight levels, and maintain normal oxygensaturation. In pregnancy, this increasesthe risk to the fetus in case the oxygensupply fails. Somewhere above 20,000 ftmsl, you will pass out quickly when thishappens.The fetus in an unconscious hy-poxic mom in this situation would seemto be in a terrible spot of trouble.

The idea behind risk-taking is to avoidharm that's irremediable, which is a realpossibility in Class A airspace, and hard-

Soaring • June 2013

ly likely below that, because it's possibleto descend quickly if the oxygen fails.Having said that, you will want an indi-cator of failure. For this reason, I preferthe Mountain High system, with whichyou get a reassuring little puff in yournostrils with each breath.

Tobacco-induced hypoxiaI've never met a woman pilot who

smoked, so perhaps this isn't necessary.Fundamentally, smoking causes hypoxiain several ways. It decreases blood flowto the uterus and placenta, its carbonmonoxide decreases the blood's oxygen-carrying capacity for both mother andfetus, and it causes degradation of thequality of the placenta.

Risks Near TermOn one hand, pregnancy is a normal

condition, not a disease. On the otherhand, there are many risks, especiallynear its end, where the physiologicmechanisms are near their natural limits.At this point, it's not necessarily altitudeexposure or cockpit posture that affectthe decision to fly. You should take intoaccount all the activities involved, on theground as well as in the air.

It may indeed be OK for you to fly un-til you go into labor. However, that's nota question we can answer in an informalessay like this one.

Inconveniences and Annoyances ofPregnantly Piloting sailplanes

Risks aside there are some annoyancesinvolved in taking your own fetus for aride in the glider.

AwkwardnessOne of God's great gifts to gravid

girls is that their gravity remains centralwhile their girth becomes greater. So theplane's CG won't shift, and pregnancyisn't going to take it meaningfully overgross. But you will feel clumsier on theground. Hoisting yourself in and out ofthe cockpit might create more audienceinterest than you want.

Fluid managementPregnancy-associated urinary fre-

quency is always annoying and will bemuch worse when you cool off duringthe climb, due to the phenomenon of"cold diuresis" that I have written about.

This is not a danger to the fetus un-less you hold it until your bladder pops,which is very painful and might distractyou from safe flying. The anesthesia andsurgery to repair it is definitely a smallbut real risk for the fetus.

Solving the bladder problem, whengravid, is probably best done with a dia-per. Use a high-capacity one, and let theurine go frequently, in small voids, be-cause diapers are not designed to handlea flood; they are designed to soak up lotsand lots of little leaks. I confess that Ihave trouble with this one, because Idon't like to be wet, and I frankly, havetrouble relaxing my well-trained sphinc-ter while thermaling. So I have to reallyconcentrate to let any urine out. Yourmileage may be different. You havea shorter spigot, but the same socialinhibitions.

You should not use self-catheteriza-tion while pregnant because there isan increased risk of urinary tract infec-tion with catheters, which pose a smallbut definite risk to the pregnancy. Mostpeople aren't willing to do this anyway,but I mention this to be complete.

An Air Force study done by Col. TracySmart, MD, showed that if the zipper ofthe flight suit goes all the way down un-der one's bottom, and the urine bag andtubing were hooked up to a neonatal re-suscitation face mask (the "nose" is heldat the back of the perineum), that thisworks just fine in a fighter jet. But thisinvolves use of the autopilot, which yourglider most likely does not have.

I personally have found that fussingaround with portable urine-collectionaids while thermalling does not improvecoordinated flight, which would be ahazard for the fetus and its mother, andto fellow pilots, in a gaggle.

Speaking of which, there is no reasonnot to be in a glider wiggling your wristand toes right up to term. After all, it'shardly more strenuous than sitting in achaise longue. If your blood pressure goesup during pregnancy, your doctor mightprescribe bed rest. And what better wayof getting bedrest than in the recumben-cy of the glider cockpit, relaxing happily- and reducing your blood pressure - bydrifting in peaceful circles near cloud-base? Who knows, this may becomestandard treatment for pre-eclampsiaafter your own success becomes known.

In-flight LaborIf you go cross-country after the 35th

week or so, you might include in yourlandout alternatives' airstrips conve-niently near obstetrical units. It wouldbe inconvenient for piloting excellenceto be delivering a child vaginally duringapproach to landing, and would likelypresent some risk for unsafe flying ifthis happens. (I assume you are flying asingle-seater in giving this advice.)

I would suggest that if contractionsbegin, you should plan to land if thecontractions are closer than 5 minutesapart if this is your first child or 10 min-utes apart if this is your second or sub-sequent pregnancy. This all depends, ofcourse, on how fast your previous deliv-eries went, and whether your husband iswaiting with the car idling on the ramp,and whether there is someone to putaway the glider for you after you land.

Contractions can be pretty distract-ing, so if they begin while in flight,you should probably just come straighthome. I don't want to be harsh aboutthis, and you know that Braxton-Hickscontractions probably won't lead to any-thing, so if they're mild and sporadic,you can probably finish the contest task.

Having said this, if you can find anOB that is a soaring pilot, in a side-by-side motorglider with an autopilot, thismight be a chance to make medical andsoaring history. We would have to makea whole new FAI category (feminine):"Free distance while in labor."The prob-lem might be how to record the onset oflabor and time of delivery on the .igc file.

ReferencesFrom the University of Colorado

School of Medicine, Children's Hos-pital, Denver - Susan Niermeyer. Thepregnant altitude visitor. Adv. Exp. Med.Biol. 1999; 474:65-77.

"The human fetus develops nor-mally under low-oxygen conditions.Exposure of a pregnant woman to thehypoxia of high altitude results in ac-climatization responses which act topreserve the fetal oxygen supply. Thefetus also utilizes several compensatorymechanisms to survive brief periods ofhypoxia. While fetal heart rate moni-toring data during air travel suggest nocompromise of fetal oxygenation, exer-cise at high altitude may place further

stress on oxygen delivery to the fetus.The limited data on maternal exercise athigh altitude suggest good tolerance inmost pregnancies; however, short-termabnormalities in fetal heart rate andsubsequent pregnancy complicationshave been observed, as well. A surveyof Colorado obstetrical care providersyielded a consensus that preterm laborand bleeding complications of pregnan-cy are the most commonly encounteredpregnancy complications among high-altitude pregnant visitors. Dehydration,engaging in strenuous exercise beforeacclimatization, and participation inactivities with high risk of trauma arebehaviors that may increase the risk ofpregnancy complications. Medical andobstetrical conditions which impairoxygen transfer at any step between theenvironment and fetal tissue may com-promise fetal oxygenation."

Jay F. Storzl and Hideaki Moriyama.Mechanisms of Hemoglobin Adapta-tion to High Altitude Hypoxia. HighAlt Med Biol. 2012 Tun; 13(2):73-81.doi: 10.1089/ham.2012.1021

"The effects of altitude on pregnancyhave been extensively studied in high-altitude residents, but there is a lack ofknowledge concerning the pregnant alti-tude visitor. Exposure to hypoxia resultsin physiologic responses which act topreserve maternal and fetal oxygenation.However, these reactions are limited andmaternal/fetal complications may beobserved, especially in association withexercise. Certain preexisting conditionsor risk factors of hypertension/pre-ec-lampsia and/or fetal growth restrictionare contraindications for traveling tohigh altitude, especially after 20 weeks.The acclimatization process has to berespected to avoid acute mountain sick-ness without taking drugs, and at least afew days of acclimatization are requiredbefore exercising."

John B. West. Human responses toextreme altitudes. Integrative and Com-parative Biology, volume 46, number 1,pp. 25-34 doi:10.1093/icb/icj005

"It is a strange coincidence that thehighest point on Earth is very close tothe limit of human tolerance to hypoxia.The physiological changes that allowhumans to reach these extreme altitudesinvolve enormous alterations of theirnormal state."

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