The Risks of Diving While Pregnant Reviewing the Research Should a pregnant woman scuba dive? Whether expectant women should dive is a question that affects not only female divers but also their partners, dive buddies and dive professionals. Most divers can recall from their open water training that women are encouraged to stop diving during pregnancy, but few classes go into further detail. What are the risks of diving while pregnant? What is it about scuba diving that is dangerous for a developing foetus? The published literature provides a foundation for the discussion. David Haas Photo BY HEATHER E. HELD, BS AND DR. NEAL W. POLLOCK, PHD s with all research, there are TABLE 1: Depth (approx) at oxygen partial pressure limits for humans limitations on how much the available studies can tell us. For Aethical reasons, experiments with pregnant women are very limited. Most studies conducted with humans are surveys, and surveys have weaknesses, most importantly that they are not as easily controlled as laboratory research and that they can easily be biased. A survey of female divers who had and the foetal circulatory system Foetal rat hearts have proven sensitive recently given birth included 69 women interact. to multihour HBO exposure (3.0 ATA who had not dived during their for eight hours), albeit of a magnitude pregnancies and 109 women who had. A range of developmental in excess of what humans could The nondiving women reported no abnormalities have been associated with tolerate. In almost half the cases, the birth defects, while the diving women hyperbaric exposure. These include low septum, which divides the right and left reported an incidence of 5.5 percent.7 birth weights among the offspring of sides of the heart, failed to form To provide perspective, the survey diving mothers14,15,26; foetal abortion28; properly20. Major blood vessels were author stated that the latter rate was bubbles in the amniotic fluid13,25; positioned incorrectly just as often, within the normal range for the premature delivery14; abnormal skull compromising normal circulatory national population. The small sample development11,15,16; malformed patterns20. size and the likelihood of selection bias limbs11,15,16; abnormal development of in those responding to the survey make the heart16,20; changes in the foetal Another study of HBO-exposed rats the results even more difficult to circulation2; limb weakness associated found no significant differences interpret. with decompression illness21; and between offspring from mothers that blindness14. had dived and offspring from mothers 6 While surveys can establish correlations, that had not dived . The PO2 in this they cannot confirm causal We expose ourselves to hyperbaric study (1.3 ATA for 70 minutes) was relationships. In this case, they cannot oxygen - that is, oxygen concentrated significantly less than that used in the confirm that diving caused a defect. by pressure - during almost all dives. previous study. The treatment To obtain such data, scientists rely on A safe limit for the partial pressure of difference may explain the dissimilar results. more highly controlled animal studies. oxygen (PO2) is frequently accepted as 1.4 to 1.6 atmospheres of absolute 19 'Diving' in chambers pressure (ATA) . Table 1 shows the Table 2 shows a summary of the depth (in msw) where these PO levels timeline for human foetal development. Hyperbaric chambers, which can 2 are achieved with different breathing It appears that hyperbaric exposure can simulate the increased pressure of gas mixtures. alter the signals foetal tissues rely on to diving, have been used to test different correctly orchestrate developmental species of animals. Those results must Rodents, which have large litters and processes. The nature of the then be translated to the human relatively short gestational periods12, abnormality is influenced by the timing experience. have been used to study the effects of of the insult. It is important to note, HBO on developing foetuses. Female however, that exposure will not affect Many complex processes occur during hamsters experiencing untreated DCI development in all instances. pregnancy, and insults (disruptions of had offspring with severe limb and skull normal events) can lead to varied abnormalities.15,16 Pregnant hamsters complications. Most diving-related Decompression stress experiencing HBO-treated decom- studies have addressed the first and The relative risk of decompression pression illness also bore offspring with third trimesters of pregnancy. First stress on mother and foetus is another defects, though with less frequency than trimester research has concentrated on question for consideration. Given the untreated group15. Neither study the teratogenic, or birth-defect-causing, sufficient decompression stress, blood reported noticeable differences in effects of hyperbaric oxygen (HBO). returning to the heart from the body anatomical development between Third trimester research has examined may contain venous gas emboli (VGE offspring from the nondiving control 23 the effects of decompression sickness or bubbles) . Sheep have been studied group and the group that dived without frequently because of the similarity (DCS) on the foetus and how diving 15,16 developing signs of DCI . between sheep and human placentae. TABLE 2: foetal developmeent during pregnancy unintentionally be induced by (modified from WebMD21 and the March of Dimes16 websites) prolonged use of indomethacin, a drug commonly used to halt premature labor9. Whether scuba diving could induce problematic closure is uncertain, but the possibility should be considered. Practical considerations In addition to possible risk to the foetus, changes in a woman's body during pregnancy might make diving more problematic. Swelling of the mucous membranes in the sinuses could make ear clearing difficult8,10, and nausea may increase discomfort10,27. The physical aspects must also be appreciated. A woman's growing abdomen could pose a problem in fitting suits, buoyancy compensation Foetal sheep whose mothers shunts), and gas exchange occurs devices, weight belts and other underwent decompression dives through the placenta. Thus, pulmonary equipment. In addition to the hazards (following U.S. Navy dive tables) filtration of bubbles does not occur inherent in poorly fitted gear, diving sometimes formed bubbles even when within the foetus. This may increase the simply may not be enjoyable. the mothers showed no signs of risk of arterial gas embolism (AGE), DCI13,21. with potentially devastating Decisions consequences. Sifting through the published literature When the ewes did develop signs of reveals why there is debate over the DCI, the foetuses demonstrated even Foetal circulation requires further topic. Data are limited and, in many more dramatic evidence of affliction. consideration. During a series of dives cases, apparently inconsistent. While Researchers reported being able to tell that exposed ewes to 100 percent this makes drawing conclusions more that a foetus had bubbles by detecting oxygen at 3.0 ATA for approximately difficult, it should not be surprising. early cardiac arrhythmias21. For the 50 minutes, researchers noticed that the foetus, these abnormal heartbeats circulatory shunts began to close while Science is very rarely as clear-cut as could be life-threatening. The offspring at depth. Flow through the foramen might be desired. It is difficult to design of some sheep that were dived late in ovale dropped by 50 percent, and the an ethical experiment that tests only the pregnancy showed limb weakness and ductus arteriosus flow fell to zero or variable of interest and controls for all spinal defects associated with DCI, even reversed direction2. others. It is the researcher's job to even when the mother had remained design the best experiments possible, symptom-free21. Once the dives were completed, the and it is the individual's or advocate's circulation reverted to its usual form, responsibility to examine the results Scientists have long known that so- and the researchers did not notice any and decide how to best respond to called 'silent bubbles' - those not negative effects from the temporary them. associated with symptoms - can change. Whether the foetus suffered develop after diving (note: Dr. Albert consequences that were not obvious to The question of diving and pregnancy Behnke, a pioneer in modern diving the researchers was unclear. is a difficult one to study since the trend medicine and physiology research, is is for women to refrain from diving credited for coining this term4). Fully The animal study data can be compared while pregnant 24. Most physicians treat functional lungs are extremely effective with human experience. Premature diving as they would any drug for in filtering bubbles from the closure of the ductus arteriosus during which the evidence with respect to circulation. In the foetus, however, human pregnancy has been associated pregnancy is incomplete: If there is not most blood bypasses the lungs (via the with congestive heart failure1,3,18 and a good reason to take it, avoid it. foramen ovale and ductus arteriosus neonatal death3,5,18. Such closure can Alert Diver Asia Pacific 30 Anyone who inadvertently dives while pregnant, however, may take solace in References the anecdotal evidence from women 1. Arcilla RA, Thilenius OG, Ranniger K. 16. Gilman SC, Greene KM, Bradley ME, reporting repeated diving during Congestive heart failure from suspected ductal Biersner RJ. Fetal development: effects of pregnancy without complication. closure in utero. Journal of Pediatrics simulated diving and hyperbaric oxygen 1969;75(1):74-8. treatment. Undersea Biomedical Research There is certainly insufficient evidence 2. Assali NS, Kirschbaum TH, Dilts PV Jr. 1982;9(4):297-304. to warrant termination of a pregnancy. Effects of hyperbaric oxygen on 17. How your baby grows [Online]. 2006 Moreover, if emergency hyperbaric uteroplacental and fetal circulation. [cited 2006 Jul 11]; Available from: URL: oxygen is required during pregnancy, Circulation Research 1968;22(5):573-88. http://www.marchofdimes.com/pnhec/ for example to treat carbon monoxide 3. Becker AE, Becker MJ, Wagenvoort CA.