Diving and Pregnancy

Caroline Fife points out in her article in this issue of theJournal of Travel Medicine that 30% of today’s divers in the US, who dive for sport, are female. Though few research studies and surveys exist on the topic of pregnancy and hyperbaric exposure, meager gleanings do point to the opinion that pregnancy should contraindicate diving. Dr. Fife mentions pertinent articles by Bolton, Bangasser, Turner, and her own recent attempts to gather more data on the contraindications to diving during pregnancy. It is encouraging to the clinician, though not to those attempting to accumulate research statistics, that there has been a dramatic decline in the percentage of respondents who continue to dive after confirmation of pregnancy. Despite scant retrospective data and the absence of any prospective studies, agencies such as the Diver Alert Network (DAN), diving doctors, and diving instructors are attempting to get the message across to the diving public that, if pregnant, women should not dive. If we reach beyond the articles confined to diving and pregnancy and make a broader review of the hyperbaric medical literature, research and studies are plentiful, and these detail the shortand long-term hazards of diving. The implication is that subtle yet profound damage may be caused by diving during pregnancy. Osteonecrosis of bone can occur after only one diving accident. Evidence obtained from a personal communication from Charles Lehner of the University of Wisconsin suggests that just one episode of missed decompression has the potential to damage the microvasculature of bone. Similarly, one missed decompression might cause vascular lesions in the maternal uterine-placental unit, which has the potential to injure tissues like the CNS of the fetus, who is a passive passenger at depth. Doctors unfamiliar with diving sometimes tell women that limited diving will limit risk. However, dangerous gas bubbling is not prevented by occasional diving. Recommendations to perform only one dive a day are not wise and would not reduce risk to zero. Diving, even at shallow depths, increases the partial pressure of 0, in all tissues and in utero. Via baroreceptor action, the subsequent increase in PO, causes neonatalization of the fetal circulation. In the short-term exposures described in animal studies by Assali and Kirchbaum, blood flow pattern reverted to a normal fetal distribution on return to normobaric conditions. However, no data are available on the effects of long-term and/or repeated hyperbaric exposures. These original researchers speculated that repeated exposures to high levels of partial pressure of oxygen may result in persistence of neonatal circulation in utero and to premature closure of the ductus arteriosis, with concomitant abnormal fetal blood distribution. If the ductus arteriosis remains constricted or closed for a significant period of time post diving, accompanying changes in the distribution of well-oxygenated hemoglobin in the fetus might result in lower 0, tensions in critical tissues and, perhaps, undetectable but subtle central and peripheral nervous damage. This would become evident later as minimal cognitive and motor function deficits appear during early childhood. The only human data on repeated exposure to hyperbaric oxygen (HBO) come from pregnant women treated for carbon monoxide (CO) poisoning. No adverse fetal outcomes have occurred in the cases where mother and fetus have both survived CO insult and therapy. Obviously, a very strong imperative exists compelling and justifying HBO exposure after CO poisoning. Fetal hemoglobin binds more strongly to CO than does adult hemoglobin, and hyperbaric exposure, even with its unknown risks, is clearly justifiable in such cases. Diving, however, is an elective sport for most participants, and the risks, even if small, are not justified during gestation since no therapeutic benefits accrue to either mother or fetus. Physicians not involved in hyperbaric medicine often disregard basic physical laws which apply to gases. Though most diving accidents involve minor