highlighted topicsPhysiology of a Microgravity EnvironmentSelected Contribution: Effects of spaceflightduring pregnancy on labor and birth at 1 G

APRIL E. RONCA1 AND JEFFREY R. ALBERTS2

1Life Sciences Division, National Aeronautics and Space Administration Ames Research Center,Moffett Field, California 94035; and 2Department of Psychology,Indiana University, Bloomington, Indiana 47405Received 3 May 2000; accepted in final form 30 May 2000

Ronca, April E., and Jeffrey R. Alberts. Selected Con-tribution: Effects of spaceflight during pregnancy on laborand birth at 1 G. J Appl Physiol 89: 849–854, 2000.—Theevents of parturition (labor, delivery, maternal care, placen-tophagia, and onset of nursing) were analyzed in femaleNorway rats (Rattus norvegicus) flown on either 11- or 9-day-long spaceflights beginning at the approximate midpoint oftheir pregnancies. Each space shuttle flight landed on the20th day of the rats’ pregnancies, just 48–72 h before partu-rition. After spaceflight, dams were continuously monitoredand recorded by time-lapse videography throughout the com-pletion of parturition and onset of nursing (days 22 and 23).Analyses of parturition revealed that, compared with groundcontrols, flight dams displayed twice the number of lordosiscontractions, the predominant labor contraction type in rats.The number of vertical contractions (those that immediatelyprecede expulsion of a pup from the womb), the duration oflabor, fetal wastage, number of neonates born, neonatal birthweights, placentophagia, and maternal care during parturi-tion, including the onset of nursing, were comparable inflight and ground control dams. Our findings indicate that,with the exception of labor contractions, mammalian preg-nancy and parturition remain qualitatively and quantita-tively intact after spaceflight during pregnancy.

parturition; microgravity; uterus; abdominal muscle; fetus;newborn; rat

THE VARIOUS PROCESSES COMPRISING mammalian preg-nancy and parturition evolved within the omnipresentcontext of the normal gravitational forces on Earth,thus raising the question of whether pregnancy andbirth can be successfully sustained in the absence ofgravity. In the only previous spaceflight in which preg-nant mammals were exposed to microgravity, rats in

late stages of pregnancy were flown on the 4.5-dayCosmos-1514 mission in 1983 (9). After this brief flight,four of five dams gave birth to viable litters. Parturi-tion was not observed systematically in the Cosmosstudy. Also, it is not known how longer flights mightaffect physiological or behavioral responses of preg-nant and parturient females and the process of birth.The most common effects of spaceflight, namely, head-ward fluid shifts, alterations in bone and calcium me-tabolism, and muscular deconditioning (5, 8, 10), mayprovide formidable obstacles to sustaining the gravidstate in space and impede the ability of mothers to givebirth.

Of particular concern are the potential effects ofspaceflight muscle deconditioning on the musculatureof pregnant dams in the days preceding parturition.For example, expulsion of the conceptus may be com-promised because of deconditioning of the transverseabdominus, an antigravity muscle in tetrapods (6).

Much is known about parturition in the Norway rat(Rattus norvegicus) (4, 14, 15). At the time of birth, thefemale rat’s behavior is centered on the processes ofdelivery and the products of birth, namely, the fetuses,placentas, and birth fluids (8). The entire process be-gins just a few hours before birth with the transitionfrom infrequent, low-amplitude uterine contractions toregular, more intense contractions. This shift signalsthe onset of labor (4, 15). Direct measurements ofintrauterine pressure in rats suggest that, near partu-rition, the rat fetus is exposed to contractions ap-proaching 20 mmHg (7). We previously described andquantified labor and delivery in the rat using 24-htime-lapse videography (15). Several behaviorally dis-tinct types of uterine contractions can be observed

Address for reprint requests and other correspondence: A. E.Ronca, Life Sciences Division, Bldg. 261, Rm 111, NASA AmesResearch Center, Moffett Field, California 94035 (E-mail:aronca@mail.arc.nasa.gov).

The costs of publication of this article were defrayed in part by thepayment of page charges. The article must therefore be herebymarked ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734solely to indicate this fact.

J Appl Physiol89: 849–854, 2000.

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during labor. During a lordosis contraction, the damlies on her ventrum and elongates her body, oftenarching her back and elevating her outstretched hind-limbs off the ground. More than 70 lordosis contrac-tions may be observed during a typical birth, at inter-vals less than 35 s apart during the last hour of labor.Lordosis contractions predominate before the birth ofthe first pup and are believed to transport the concep-tus into the lower birth canal. Vertical contractions,observed just before the birth of a pup, consist of aseries of rapid, bilateral abdominal lifts. Rat damstypically deliver from 8 to 12 pups over a period of40–140 min. Elements of maternal behavior, such aslicking and retrieving, emerge when the first pup isexpelled from the womb. At birth, the mother licks theneonate, removing its birth membranes, thereby help-ing to initiate postnatal breathing (13). The onset ofnursing occurs soon after the last pup is born.

In the present experiment, we tested hypothesesthat mammalian pregnancy and parturition can sur-vive exposure to sustained periods of spaceflight. Onthe basis of the brief Cosmos-1514 mission, we pre-dicted that pregnant rats flown on longer (11 and 9day) missions would also complete their 22-day preg-nancies and undergo vaginal deliveries but that partu-rition would not be successful for all rat dams. Thelonger period of spaceflight exposure relative to theCosmos mission was predicted to increase fetal lossesand reduce the number of live births. We predictedspecific effects on labor contractions at the time ofparturition, mediated via spaceflight-induced changesin uterine contractile proteins (3) and abdominal mus-culature (6). We also hypothesized that labor contrac-tions would be less effective after spaceflight exposure,possibly lengthening the birth process. We also pre-dicted postflight behavioral changes such as reducedappetite and lethargy and thus quantified the dams’postflight feeding, drinking, and locomotion. Charac-teristic maternal responses to the young during partu-rition were analyzed to test the hypothesis that pat-terns of maternal care would be disrupted afterspaceflight.

The data presented are derived from two spaceflightmissions jointly sponsored by National Aeronauticsand Space Administration (NASA) and National Insti-tutes of Health (NIH) and are called the Rodent 1(NIH.R1) and Rodent 2 (NIH.R2) missions. Ten ratdams were flown on each mission, launched at theapproximate midpoint of pregnancy [gestational day(GD) 9 for NIH.R1 and GD11 for NIH.R2] and landedclose to the time of parturition (GD20 of the rat’s22-day pregnancy). The mission lengths were 11 and 9days, respectively. The dams on each flight weretreated similarly. Continuous postflight video surveil-lance of both NIH.R1 and NIH.R2 rat dams, includingtime-lapse recordings of labor and delivery, permittedus to replicate the parturition analyses. This was par-ticularly important because the NIH.R1 study involvedperforming a unilateral hysterectomy on each damsoon after recovery on GD20, the major difference be-tween the two flights. This was done so that both fetal

and neonatal samples could be obtained from each ofthe NIH.R1 subjects (1).

MATERIALS AND METHODS

Subjects. Forty nulliparous, pregnant Sprague-Dawleyrats (Taconic Farms, Germantown, NY) weighing between165 and 205 g were used. The time-bred dams were shippedto Kennedy Space Center (KSC) on GD2 (spermatozoa posi-tive 5 GD1). Animals were housed in a room with controlledlighting (6 AM to 6 PM) and temperature (;22°C). Pregnantrats were housed individually in standard vivarium cages (47cm 3 26 cm 3 21 cm) with corncob bedding material. Ratchow and water were available ad libitum. All animal proce-dures adhered to NASA guidelines and the NIH Guide for theCare and Use of Laboratory Animals. [DHHS Publication No.(NIH) 85-23, Revised 1985, Office of Science and HealthReports, Bethesda, MD 20892].

Treatment of dams. Two treatment groups were used inthese experiments. For each study, 10 dams were housed ingroups of five in flight animal modules (described in Surgicallaparotomy of the NIH.R1 and NIH.R2 dams, below) andexposed to launch, spaceflight, and landing (flight group).Synchronous control dams (n 5 10) were treated identicallyto flight animals but were not exposed to launch, landing, orspaceflight. These animals were run at the same gestationalages as the flight group but with a 24-h delay relative to theflight group to allow time for downlinking from the shuttle ofthe previous day’s environmental conditions. In this way,environmental parameters (i.e., temperature, humidity, andexposure to augmented lighting during video recording) on-board the shuttle could be mimicked for the synchronouscontrol group. The preflight (12:12 h) light-dark cycle wasmaintained in the housing for both the flight and groundgroups. Before flight, dams were carefully matched accordingto weight across flight and synchronous control conditions.

Maternal surgeries. All experimental dams sustained twosurgical procedures during the study (described below). OnGD7, surgical laparotomy was performed to confirm preg-nancy and establish the number of implantation sites. Damswere selected for inclusion in the study only if a minimum offive embryos populated each of their paired uterine horns. OnGD20, immediately after recovery from the space shuttle, theNIH.R1 dams (but not the NIH.R2 dams) were given aunilateral hysterectomy under anesthesia, yielding for im-mediate analysis of fetuses from all 10 dams (i.e., n 5 10).The same dams then recovered from anesthesia, completedgestation, and underwent vaginal delivery of pups from theremaining uterine horn, thereby providing neonates for post-natal analyses (n 5 10). The NIH.R2 dams were eitherobserved until birth (n 5 6) or dissected on recovery (n 5 4).Only the dams that underwent parturition are discussed inthis report.

Surgical laparotomy of the NIH.R1 and NIH.R2 dams.Laparotomy was conducted on flight and synchronous controldams under aseptic conditions on GD7, the earliest day onwhich implantation sites (decidual swellings) can be reliablyvisualized. This procedure is described elsewhere (1). Briefly,the dam was anesthetized with isoflurane (IsoFlo, AbbottLabs, North Chicago, IL) vapor using a nonrebreathing ro-dent anesthesia unit (Viking Products, Medford Lakes, NJ).The fur overlying the abdomen of the anesthetized rat wasshaved, the skin was cleansed with antiseptic and alcohol, aveterinary opthalmic ointment was applied, and an antibioticand analgesic mixture [Microcillin, Anthony Products, Arca-dia, CA (10,000 IU) and butorphanol tartrate, Fort DodgeLabs, Fort Dodge, IA (10 mg/kg)] was given by subcutaneous

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injection. An incision was made, beginning ;2 cm cranial tothe pubis and extending cranially 2–3 cm. Each uterine hornwas gently grasped between decidual swellings and gentlyexternalized for close visual inspection and counts of implan-tation site, which were recorded. The uteruses were carefullyreinserted into the abdominal cavity, after which interruptedsutures were used to close the peritoneum and muscle layer.The overlying skin was then closed with 9-mm wound clips.The entire procedure lasted 10 min.

On GD8 for NIH.R1 and on GD10 for NIH.R2, the flightand synchronous control dams were housed in groups of fivewithin an animal enclosure module (AEM), which is NASA’sflight cage for group-housed adult rodents. The animal cham-ber portion of the AEM is a stainless steel mesh cage,;23.5 3 35.6 3 21.6 cm (in Earth-gravity orientation). Foodwas available in the form of food bars, each about 2.5 3 2.5 320 cm, which were attached to the walls of the AEM. Thesefoodbars are fabricated from a commercial diet (Teklad Diets,Madison, WI) and are nutritionally complete and resistent tospoilage. Water was available from any of four Lixit valvesthat protrude from a 21 3 11.1 3 15.2 cm stainless steel boxwithin the AEM. With the water system and food bars inplace, the AEM is a compact volume for five pregnant rats.Airflow through the AEM is controlled by external fans thatcreate a near-laminar flow moving from ceiling to floor (innormal Earth gravity orientation); the effluent airstreammoves through the waste tray containing activated charcoaland absorbent filter.

Unilateral hysterectomy of the NIH.R1 dams. The purposeof the unilateral hysterectomy was to provide a sample offetuses soon after return from spaceflight (see Ref. 1 forfurther background and discussion of the rationale). Within3 h after recovery from spaceflight, the first flight dam wasanesthetized. Anesthesia and surgical preparations wereidentical to those described for the laparotomy procedure onGD7. The uterine horns were exteriorized by extending themidventral abdominal incision. The uterine horn removedwas alternated across rats in each treatment group. The hornwas ligated cranially and caudally with braided silk (20,Ethicon, Somerville, NJ) and then excised. The incision wasclosed by following the procedures used for laparotomy.

Video recording of labor and birth. Within several hours ofboth recovery and unilateral hysterectomy (NIH.R1) or re-covery (NIH.R2), the dams were housed singly in Plexiglasobservation cages (12.5 cm 3 8.5 cm 3 9.25 cm) lined withcorn cob bedding and placed in a vivarium. Food bars wereplaced on the cage floor, and Lixit spouts were positionednear the base of the cage to facilitate the mothers’ access tofood and water. Daily records of food bar consumption, waterintake, and body weight were maintained for the remainderof the study. The dams were videotaped continuously begin-ning soon after recovery until the completion of parturitionand the onset of nursing. A mirror was angled at the rear ofeach observation cage to permit camera views from both thefront and rear of the cage. Cages were positioned four percamera view. Red lighting was illuminated during the darkphase to enable 24-h video data collection (12:1 record-to-playback ratio).

Data analysis. Video data were analyzed by trained scor-ers during real-time playback of the videotapes time locked toa computerized event-scoring program (13). Briefly, theamount of time dams spent feeding, drinking, or ambulatingwas quantified with the use of this system. Interrater reli-ability (IRR) for these measures was R2 . 0.99. The numberand duration of labor contractions, number of neonates born,placentophagia (ingestion of placenta), the total duration ofbirth, maternal care (licking and handling of neonates), and

the onset of nursing were also encoded from the video record-ings (IRR was R2 . 0.98). Individual data were expressed aslitter means and analyzed with the use of ANOVA, t-tests, orsimple regression.

RESULTS

NIH.R1 and NIH.R2 dams at recovery. Because ofinclement weather, the shuttle carrying the NIH.R1payload landed at the Hugh Dryden Flight ResearchFacility (HDFRF) alternate landing site in California.Within 3 h of landing, the rats were delivered to thepayload receiving facility. The dams were then care-fully unloaded from the AEMs, given a health exami-nation, and weighed. Dam body weight gains at shuttleload and unload were identical in the flight and syn-chronous control groups (percent change from GD9 toGD20 as follows: flight 5 45.7 6 2.0 and synchronouscontrol 5 42.4 6 1.7%; not significant). All of the damswere deemed to be in good condition. Unilateral hys-terectomy was performed on the flight group damswithout complication. Over the next several hours, thedams showed characteristic signs of recovery from gen-eral anesthesia and surgery.

The NIH.R2 payload landed at KSC. Within 3–4 h oflanding, the dams were given postflight health checksand weighed. NIH.R2 dam body weight gains at shut-tle load to unload were significantly different in theflight and synchronous control groups [percent changefrom GD11 to GD20 as follows: flight 5 23.8 6 1.0 andsynchronous control 5 28.6 6 1.0%; t(18) 5 24.1, P ,0.001]. Six flight dams and six synchronous controldams entered nest cages without manipulation.

Readaptation of flight dams to 1 G. In contrast to theNIH.R1 dams, which received postflight surgery (i.e.,unilateral hysterectomy), data from the NIH.R2 damsprovide an unbiased perspective of the effects of space-flight on pregnant mothers’ behavioral readaptation to1 G. These data are shown in Fig. 1. Results of thetime-lapse analyses are presented across three consec-utive 12-h time intervals beginning with the darkphase of the circadian cycle on GD20 [corresponding torecovery (R) 1 12 h (R 1 12)] and ending 36 h later (atR 1 48), coincident with the onset of the light phase ofthe cycle on GD22. This analysis revealed that flightdams ambulated less than did synchronous controldams [Fig. 1A; gravity F(1,10) 5 14.5, P , 0.01; New-man-Keuls test, P . 0.05] but only during the darkphase of the circadian cycle [time interval F(2,20) 512.5, P , 0.001; gravity 3 time interval F(2,20) 5 7.5;Newman-Keuls, P . 0.05]. During the light phase ofthe cycle (R 1 24 and R 1 36), a floor effect wasobserved that obscured potential group differences:both flight and synchronous control dams locomoted forless than 5% of the observation interval during thelights-on period. Despite the reduced activity of theflight dams during the dark phase of the cycle, theamount of time dams spent eating and drinking wasequivalent to that of synchronous dams (Fig. 1B; grav-ity F , 1), and the typical circadian rhythm of feedingbehavior was observed [time interval F(2,20) 5 29.3;P , 0.0001].

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Labor in flight dams. Dams from both flights beganlabor at the expected time (on GD22 and GD23) withthree exceptions: two NIH.R1 flight dams and onesynchronous dam did not show signs of impendingparturition by 1500 on GD23. In accordance with pre-determined project requirements, the neonates of thesedams were delivered by cesarean section. There was nocorresponding requirement for NIH.R2; however, ce-sarean delivery was performed on one dam from theflight because she appeared to be in distress duringlabor. Video failure caused data from two additionalNIH.R1 control animals to be lost. We present com-plete data from eight flight dams and seven synchro-nous control dams for NIH.R1 and from five flightdams and six synchronous control dams for NIH.R2.

Figure 2 shows the results of the labor analyses forthe two flights. Beginning 6 h before the birth of thefirst pup and throughout parturition, NIH.R1 flightdams exhibited over two times more lordosis contrac-tions than did synchronous control dams [Fig. 2, solidbars; t(13) 5 3.0, P , 0.01]. Vertical contractions wereunaffected by spaceflight [t(13) 5 0.50, not significant].Although contraction numbers differed, the averageduration of lordosis contractions was identical in thetwo groups (flight 5 19.2 6 2.0 s, synchronous con-trol 5 19.2 6 2.3 s).

Precisely the same pattern of results was observed inthe NIH.R2 dams [Fig. 2, open bars; t(9) 5 3.9, P ,0.01]. Vertical contractions did not differ across groups(not significant).

Birth. The dams successfully delivered strong andviable pups. Table 1 shows the number of decidualswellings, the numbers of neonates born, neonatalbirth weights, total duration of birth, ingestion of pla-centas (placentophagia), and maternal behavior duringparturition, as measured by licking and retrieving of

Fig. 1. Behavioral readaptation of National Institutes of Health(NIH) Rodent 2 (NIH.R2) flight and synchronous control dams to 1 G(n 5 6 per condition). Locomotion (top) and eating and drinking(bottom) across consecutive 12-h dark-light-dark periods beginningat 6 PM on gestational day (GD) 20 [recovery (R) 1 12h (R 1 12)], at6 AM on GD21 (R 1 24), and at 6 PM on GD21 (R 1 36). Locomotiondiffered across flight and synchronous dams during the dark phase ofthe circadian cycle (*P , 0.05); eating and drinking were identicalacross the groups.

Fig. 2. Top: behavioral expression of a lordosis contraction in theparturient rat dam. Bottom: number of lordosis contractions ob-served in NIH Rodent 1 (NIH.R1) (n 5 15) and NIH.R2 (n 5 12) flight(left) and synchronous control (right) dams. Observations antedatedthe birth of the first pup by 6 h and continued until the birth of thelast pup. The number of lordosis contractions observed in flight andsynchronous dams differed from one another (*P , 0.05). Note:NIH.R1 dams underwent unilateral hysterectomy before parturition.

Table 1. Number of decidual swellings, numberof neonates born, neonatal birth weights, totalduration of birth, placentophagia, and maternal care(licking and handling) of neonates during parturitionat 1 G in pregnant dams flown on the NIH.R1 andNIH.R2 missions and synchronous control dams

NIH.R1 NIH.R2

Flight Synchronous Flight Synchronous

No. decidualswellings 13.160.3 13.160.2 13.560.4 13.360.3

No. neonates born 11.860.6 11.760.6 12.560.6 13.260.4Neonatal birth

weights, g 6.160.4 6.360.6 5.960.4 5.860.4Birth duration,

min 57.8611.9 42.162.8 97.567.9 87.3617.3Placentophagia,

min 12.662.6 13.161.0 13.563.1 14.061.3Maternal care,

min 47.465.9 53.965.1 34.062.1 34.763.9

Values are means 6 SE. Neonatal birth weights were derived fromlitter averages. Birth duration data for NIH.R1 dams were affectedbecause of unilateral hysterectomy, resulting in neonates populatingonly one uterine horn. NIH.R1 and NIH.R2, National Institutes ofHealth Rodent 1 and Rodent 2.

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neonates. In contrast to our initial prediction, morbid-ity was very low. For NIH.R1, 4 of 60 pups born toflight dams and 1 of 58 pups born to synchronous damswere found dead on the day of birth. For each of theother measures, identical results were obtained forflight and synchronous conditions. The results of thetwo flights were highly consistent with each other.

DISCUSSION

The pregnant spaceflight dams returned to Earth ingood condition. For NIH.R1, weight gain of dams dur-ing flight, particularly important to the fetuses devel-oping in utero, was comparable to the weight gain ofground control dams. This finding is consistent withnormal Earth gravity body weight gains seen in adultmale rats during 14-day spaceflight missions (14).NIH.R2 flight dams gained about 5% less than syn-chronous controls, but differences were not observed inany other measure of maternal, fetal, or neonatal out-come after flight. Body weights of dams in the flightand synchronous control conditions were identical atlaunch for both flights. Because the NIH.R2 missionwas 2 days less in duration than the NIH.R1 mission,one possibility is that initial postflight weight loss wasfully regained in flight on the longer 11-day mission(NIH.R1) but not achieved by 9 days (NIH.R2). Addi-tional studies are needed to characterize profiles ofbody mass change in pregnant animals followinglaunch, on orbit, and on recovery from space.

The major finding of our analyses is that flight damshad uncomplicated, successful vaginal deliveries. Par-turition occurred at the appropriate gestational time.Number and size of the litters were equivalent to thoseof controls. Because we had noted during preflightlaparotomy the number of implantation sites in theuterine horns of each dam on the 7th day of pregnancy,we were also able to determine that fetal loss, i.e., thedifference between the number of implantations andnumber of pups born to each dam, was equivalentbetween groups. These findings were seen in both theNIH.R1 and NIH.R2 flight groups. The correspondencebetween these two data sets is striking particularlybecause the NIH.R2 dams were not surgically manip-ulated before collection of observational data.

Readaptation of flight dams to 1 G. The NIH.R2dams provided the first systematic and continuousobservational data ever collected on the postflight re-adaptation of rats to 1 G. The flight dams were gener-ally less active than the synchronous control dams, asindicated by reduced ambulation during the dark (ac-tive) phase of the circadian cycle. There were differ-ences in time spent eating and drinking between theflight dams and the synchronous controls, and bothgroups followed characteristic circadian fluctuations.The postflight reduction in the locomotor activity ofdams is analogous to that of pregnant dams undergo-ing adaptation from the normal 1 G on Earth to 1.5-Ghypergravity (14).

Labor after spaceflight. Labor contractions were af-fected by spaceflight during pregnancy. The NIH.R2

dams did not receive the abdominal surgery shortlybefore labor; therefore, their data are not confoundedin any way. Nevertheless, the pattern of results fromthe two spaceflights was strikingly clear and reliable.

Quantification of lordosis contractions encoded dur-ing playback of the video recordings revealed thatdams from both flights displayed dramatically morelordosis contractions than did synchronous controls.From the 6 h before parturition until the birth of thelast pup, flight dams had, on average, twice the num-ber of contractions compared with controls. Despitethis difference, both the number of vertical contrac-tions and the duration of visible labor were unaffected.

One interpretation of the increased number of con-tractions is that the contractions were less efficaciousin the flight animals; thus additional contractions wererequired to perform the work of moving fetusesthrough the uterus and into the birth canal. Uterinetissue analyzed from the NIH.R2 dams revealed reduc-tions in connexin 43, the major gap junction protein inmyometrium (3). Uterine levels of connexin 26, locatedprimarily in endometrial epithelial cells, were un-changed. It was suggested that decreased connexin 43alters synchronization and coordination of labor con-tractions, resulting in a requirement for more laborcontractions to complete parturition. Reports on thehistological status of the dams’ musculature providesome insight into the consequences of spaceflight de-conditioning on the abdominal muscles, many of whichserve postural (i.e., antigravitational) functions as wellas participate in the dramatic labor contractions.Fejtek and Wassersug (6) reported that certain abdom-inal muscle groups showed the kinds of decreases infiber diameter associated with unloading and weaken-ing. The transverse abdominus was among those thatreflected such loss, and weakness of this muscle groupmay have contributed to the requirement for additionalcontractions. In contrast, the external obliques did notshow the expected atrophy. The seemingly paradoxicaldifferences between these abdominal muscle groupscan be resolved by combining the anatomic results withobservations of the dams’ in-flight behavior.

We analyzed video recordings of the pregnant damsin the AEMs that were taken during flight (2). Wedevised a kinematic coding scheme by which we clas-sified and quantified the movements made by dams inspace and in the 1-G synchronous control condition.With this analytic scheme, we found that movementsinvolving pitch and yaw were approximately equiva-lent in the flight and synchronous animals. In contrast,flight dams displayed about seven times more rollingmovements than did synchronous controls. This as-tounding difference, we think, can be explained as aconsequence of the increased number of surfaces avail-able in microgravity for ambulating and crawling.Many of the movements from surface to surface involverolling movements along the rat’s body axis (the z axis).

Thus, within the weightless environment of space,the external obliques are likely to be exercised by themechanics of the dams’ rolling movements, the type ofactivity frequently observed in microgravity but rarely

853SPACEFLIGHT AND BIRTH

on Earth. In contrast, the transverse abdominus mus-cles are probably used minimally under conditions ofweightlessness, where postural control involves littleeffort; hence, these muscles are not maintained as wellas they are in the synchronous controls. During expo-sure of the pregnant females to spaceflight, decreaseduterine connexin 43 and deconditioning of the trans-verse abdominus may have synergistically reduced theeffectiveness of uterine contractions.

Birth and maternal care of neonates after spaceflight.Although more contractions may have been requiredfor parturition in the flight group, this difference didnot affect the duration or temporal patterns of birth.The flight dams appeared to be competent mothers.Maternal licking and handling of neonates during par-turition and the consumption of birth fluids and mem-branes (i.e., placentophagia) were indistinguishable inflight and synchronous control dams. Within 3 h ofbirth, mammary tissue was visually inspected andmammary gland metabolic activity was analyzed (11).These studies indicated that the dams’ were physiolog-ically prepared for lactation.

In conclusion, the NIH.R1 and NIH.R2 spaceflightexperiments provide a convincing database for the fea-sibility of studying mammalian development underspaceflight conditions. It appears that the latter half ofthe dams’ pregnancy and the offsprings’ gestation canwithstand the novel challenge of microgravity condi-tions. The maternal-fetal system is superbly adaptableindeed, for it can adjust to conditions never beforesustained during ontogenesis anytime or anywhere onEarth.

One of the most surprising findings from the spaceshuttle studies was the dams’ ability to have successfulvaginal delivery following spaceflight deconditioningfor most of the second half of the pregnancy. It must berecognized, however, that the pregnant rats were notimmune to the deconditioning effects of space. Theyshowed the typical profile of postural and locomotorsigns of postflight muscle weakening. Moreover, therewas clearly a difference in their labor contractions,indicating that we must be vigilant in future ventures,particularly with exposures of longer duration.

Observational data of the rats’ in-flight behaviorprovided insights important to understanding space-flight effects on the bodies of dams as well as identify-ing potential concerns for newborns. Labor contrac-tions during birth provide an important source ofperinatal stimulation that promotes breathing and or-ganized suckling in the neonate (13). Maternal effectson offspring are potentially significant interpretive is-sues that should be considered in future studies involv-ing mammalian development under altered gravityconditions.

We acknowledge Regina Abel, Michael Armbruster, Karen Cabell,Cheryl Galvani, Kieu Lam, Nicole Mills, Erika Roldan, and David

Tanner for assistance with data collection and analysis. We thankJoe Calabrese, Debra Reiss-Bubenheim, Paula Dumars, Carol El-land, Nichola Hawes, Dana Leonard, Vera Vizar, Sharon Yavrom,and other members of the science support team at KSC, HDFRF, andNASA Ames Research Center. We acknowledge the crews of theSTS-66 and STS-70 flights, especially mission specialist J. T. Tan-ner. We also thank the anonymous reviewers of this manuscript fortheir critical comments.

This work was supported by NASA Grants NCC2-870 andNAS121-10-40 and by National Institute of Mental Health GrantsMH-46485 and MH-28355.

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