Article reprint: Spring 1994
"Pregnancy and Diving"
By Edward H. Lanphier, M.D., Senior Scientist, Emeritus
Dept of Preventive Medicine, University of Wisconsin, Madison
-------------------------------------------------
Instead of presenting a lot of data, I want to tell you a story from the real life of diving medicine and research.
Once upon a time, there weren't any female divers except in faraway places. So pregnancy just wasn't on the list of diving medical problems. But beginning around 1950, with the introduction of practical scuba equipment, a few women began diving -- for recreation, for scientific work, and a few even for commercial purposes.
Some of these women divers wondered about diving during pregnancy and asked their doctors about it. None of the doctors really knew what to say, so the most honest ones said "I don't know." Some who knew absolutely nothing about diving said, "Why not?" and a few who knew something about diving medical problems said, "A lot of things could happen. Why take a chance?"
Some early observations with pregnant animals indicated that there might be no problem. But in 1978, a group at a Texas university got some pregnant sheep which were close to term, put Doppler bubble-detection devices on the umbilical vessels of the fetus, sewed things up, and put the mothers in the chamber. They exposed different ones to different "dry dives" on the US Navy no-stop limit curve: depths and dive-durations that do not normally require decompression stops on ascent. At 100 ft./25 min., most of the fetuses showed a lot of bubbles on decompression even though their mothers appeared to be okay. The investigators felt sure that the lambs would have died except for prompt recompression.
In animals exposed at 60 ft./60 min., everything seemed to be all right. On the basis of this one small sheep study, these university people put out press releases and a paper suggesting that it is all right for pregnant women to dive so long as they don't go deeper than 60 feet.
Not long after that, I was invited to attend an Undersea Medical Society workshop on pregnancy and diving. That was in late 1978. I was glad to be present, but I had little experience with pregnancy in divers and few opinions to offer. However, at the University of Wisconsin, we had one of the real world-class authorities on the physiology of the fetus. That was Dr. John H.G. Rankin, and Dr. Rankin was also interested in diving. So I got an invitation to the workshop for him, and we both went.
It was clear that nobody present really knew much about the topic, but the emphasis on the Texas sheep study and its publicity was especially offensive to John Rankin and me. We decided that it was important to have a new look at the question using somewhat different methods.
At Wisconsin, we had very recently acquired a fine high pressure research chamber. Dr. Rankin's regular research program involved a lot of pregnant sheep, and many of those were available for what we wanted to do. Dr. Rankin had well-tested procedures for measuring blood pressure, blood flow, and other variables in the mother, the placenta, and the fetus. We put on some extra effort and had a project going early in 1979.
A close look at one of the sheep ready for a "dive" in the chamber showed a batch of small tubes coming out through her side. These tubes had been installed in blood vessels of the mother and fetus during surgery a week or so before. Enough time had elapsed for recovery.
After all the preparations were completed, the chamber compartment was "buttoned up" and then pressurized to one of the points on the no-stop curve -- like 100 ft./25 min. Automatic chamber controls produced the dive profiles that the study required.
As soon as a simulated dive was completed, with the mother sheep back at normal "surface" pressure, the door was opened and various instruments were hooked up to recorders. Typically, the fetus seemed to be just fine at first. Then, within 15 minutes or so, the hearbeat began to be irregular, and the blood pressure started to fall. In most instances, the fetus died a few minutes later. Then the mother was anesthetized and the fetus was quickly brought out by cesarean section.
When the dead fetus was examined we always found many bubbles in the blood vessels, and the heart was always full of bloody froth. There were also many bubbles in the blood vessels of the placenta.
At this point we were just confirming what the Texas investigators had found ãexcept that our animals were in trouble even at 60 ft./60 min. Then an interesting thing happened: We had scheduled "control dives" without any instrumentation, but one of the sheep provided an even better test before we had a chance to carry out the plan. One morning, we dived a pregnant ewe carrying twins, and only one of the twins had been instrumented for the study. That twin died on schedule, but the other one was alive when it was delivered, and we found no bubbles when it was autopsied. This suggested that the instrumentation, the very minor surgery on the fetus, or something about the measuring procedure was responsible for the massive bubbling.
We studied more twin pairs, and we exposed mothers to pressure without any instrumentation at all. Uninstrumented fetuses were always free of bubbles, and those that were allowed to go to term were born normally without any evident abnormalities.
One time, twin lambs were born normally after surgery but before the scheduled dive. We clipped off the protruding tubes on the intubated lamb and sent both lambs along in the chamber when another pregnant ewe was dived. The untouched lamb had no problems, but the one with tubes still in place had a severe case of bends. Our results were published in The Journal of Applied Physiology in 1980.
There could be no doubt that the experimental procedure was somehow responsible for the bubble problems that we saw. This provides a fine example of the fact that scientific measurements can sometimes change the thing they're trying to measure. We feel quite sure that this explained the Texas results also, although that study included no "control dives" without instrumentation. In any event, neither study showed that diving to any specific depth is safe during pregnancy whether anyone meddles with the fetus or not.
A very important reason for caution has to do with the arrangement of blood circulation in the fetus. The big difference from the adult is that the fetus does not yet use its lungs, so little blood goes to them. Uptake of oxygen and removal of excess C02 takes place in the placenta instead of the lungs.
In adult animals and humans, the lungs not only take care of gas exchange with the environment but also serve as a "full-flow filter" for the blood, removing bubbles and Ietting them disappear harmlessly. In the fetus, most of the blood bypasses the lungs through the foramen ovale or the ductus arteriosus, channels which normally close when the baby is born and the lungs start functioning. In the fetus, without filtration in the lungs, bubbles that form for any reason whatsoever can circulate freely and may lodge in some vital organ such as the brain or heart muscle. In some adult humans, the foramen or the ductus has failed to close normally; and these individuals are at unusual risk much like thc fetus, from bubbles that form following a dive.
We once thought that bubble formation isn't as likely to occur in the fetus as in the mother -- so that the fetus might be all right even if the mother developed decompression sickness. In a study that we conducted at Wisconsin for another purpose, we made simulated dives repeatedly with a lot of sheep. All of them had mild bends on at least two occasions. Some of the ewes became pregnant during the study, and most of them delivered nice, normal lambs. But the number of stillbirths was much higher than normal, and all of these fetal deaths followed a "bends event" in the mother. No lambs were born alive to mothers who had decompression sickness following the last dive before delivery.
Going back to the Undersea Medical Society workshop in 1978, one of the most constructive participants was a young nurse from Florida, Margie Bolton. She was in the midst of conducting a questionnaire survey of women divers who had been pregnant. When the results of her study came out in 1980, the most alarming finding was that 5.5 percent of babies born to mothers who had continued diving during pregnancy had birth defects against none in those whose mothers had stopped diving.
Five percent is not far from the overall national average for birth defects in general; and surveys like Margie's are open to a lot of questions. Nevertheless, there is reason for a lot of concern about the possibility of causing developmenal defects tha would arise very early --perhaps even before a woman realized that she was pregnant. Margie Bolton came to the University of Wisconsin to work on a Ph.D. in physiology under Dr. John Rankin. Among other things, she conducted a study involving 40 pregnant ewes, half of which made repeated dry dives during the crucial 12-40 day period when most development of parts and organs takes place in the sheep fetus. Margie found few birth defects, and there was no significant difference between "dived" and "non-dived" animals in that respect.
While the report of her sheep study was still "in press" in a leading obstetrical journal, Margie was hurt in an accident that involved severe head injury. She has not been able to conduct any further research. A number of additional studies have been conducted by others, but whatever anyone can show in animals, it is not safe to apply the conclusions direcly to human divers.
No one is likely to conduct the sort of study that might really answer the question: to have two evenly-matched groups of female divers of child-bearing age and to encourage one group to dive during pregnancy and to ensure that the other group did not do so. From the ethical standpoint, such a study would be indefensible no matter what it showed or how important it seemed at the time.
Then what advice can we give to a diver who is or may be pregnant? All I can say now in good conscience is to stop diving if you are or may be pregnant. If you intend to become pregnant, please stop diving first. These are hard words, and surely some depths and times and kinds of diving must be all right. The problem is that no one can yet be sure what would be safe and what wouldn't. (And of course, decompression isn't the only factor in diving that might harm a fetus - or the mother.) The only thing I'm sure about now is that - until a lot more experience accumulates and gets analyzed -- anybody who tells you that such-and-such limits are safe for pregnant divers is guessing -- and may very well be guessing wrong.
"Pregnancy and Diving"
By Edward H. Lanphier, M.D., Senior Scientist, Emeritus
Dept of Preventive Medicine, University of Wisconsin, Madison
-------------------------------------------------
Instead of presenting a lot of data, I want to tell you a story from the real life of diving medicine and research.
Once upon a time, there weren't any female divers except in faraway places. So pregnancy just wasn't on the list of diving medical problems. But beginning around 1950, with the introduction of practical scuba equipment, a few women began diving -- for recreation, for scientific work, and a few even for commercial purposes.
Some of these women divers wondered about diving during pregnancy and asked their doctors about it. None of the doctors really knew what to say, so the most honest ones said "I don't know." Some who knew absolutely nothing about diving said, "Why not?" and a few who knew something about diving medical problems said, "A lot of things could happen. Why take a chance?"
Some early observations with pregnant animals indicated that there might be no problem. But in 1978, a group at a Texas university got some pregnant sheep which were close to term, put Doppler bubble-detection devices on the umbilical vessels of the fetus, sewed things up, and put the mothers in the chamber. They exposed different ones to different "dry dives" on the US Navy no-stop limit curve: depths and dive-durations that do not normally require decompression stops on ascent. At 100 ft./25 min., most of the fetuses showed a lot of bubbles on decompression even though their mothers appeared to be okay. The investigators felt sure that the lambs would have died except for prompt recompression.
In animals exposed at 60 ft./60 min., everything seemed to be all right. On the basis of this one small sheep study, these university people put out press releases and a paper suggesting that it is all right for pregnant women to dive so long as they don't go deeper than 60 feet.
Not long after that, I was invited to attend an Undersea Medical Society workshop on pregnancy and diving. That was in late 1978. I was glad to be present, but I had little experience with pregnancy in divers and few opinions to offer. However, at the University of Wisconsin, we had one of the real world-class authorities on the physiology of the fetus. That was Dr. John H.G. Rankin, and Dr. Rankin was also interested in diving. So I got an invitation to the workshop for him, and we both went.
It was clear that nobody present really knew much about the topic, but the emphasis on the Texas sheep study and its publicity was especially offensive to John Rankin and me. We decided that it was important to have a new look at the question using somewhat different methods.
At Wisconsin, we had very recently acquired a fine high pressure research chamber. Dr. Rankin's regular research program involved a lot of pregnant sheep, and many of those were available for what we wanted to do. Dr. Rankin had well-tested procedures for measuring blood pressure, blood flow, and other variables in the mother, the placenta, and the fetus. We put on some extra effort and had a project going early in 1979.
A close look at one of the sheep ready for a "dive" in the chamber showed a batch of small tubes coming out through her side. These tubes had been installed in blood vessels of the mother and fetus during surgery a week or so before. Enough time had elapsed for recovery.
After all the preparations were completed, the chamber compartment was "buttoned up" and then pressurized to one of the points on the no-stop curve -- like 100 ft./25 min. Automatic chamber controls produced the dive profiles that the study required.
As soon as a simulated dive was completed, with the mother sheep back at normal "surface" pressure, the door was opened and various instruments were hooked up to recorders. Typically, the fetus seemed to be just fine at first. Then, within 15 minutes or so, the hearbeat began to be irregular, and the blood pressure started to fall. In most instances, the fetus died a few minutes later. Then the mother was anesthetized and the fetus was quickly brought out by cesarean section.
When the dead fetus was examined we always found many bubbles in the blood vessels, and the heart was always full of bloody froth. There were also many bubbles in the blood vessels of the placenta.
At this point we were just confirming what the Texas investigators had found ãexcept that our animals were in trouble even at 60 ft./60 min. Then an interesting thing happened: We had scheduled "control dives" without any instrumentation, but one of the sheep provided an even better test before we had a chance to carry out the plan. One morning, we dived a pregnant ewe carrying twins, and only one of the twins had been instrumented for the study. That twin died on schedule, but the other one was alive when it was delivered, and we found no bubbles when it was autopsied. This suggested that the instrumentation, the very minor surgery on the fetus, or something about the measuring procedure was responsible for the massive bubbling.
We studied more twin pairs, and we exposed mothers to pressure without any instrumentation at all. Uninstrumented fetuses were always free of bubbles, and those that were allowed to go to term were born normally without any evident abnormalities.
One time, twin lambs were born normally after surgery but before the scheduled dive. We clipped off the protruding tubes on the intubated lamb and sent both lambs along in the chamber when another pregnant ewe was dived. The untouched lamb had no problems, but the one with tubes still in place had a severe case of bends. Our results were published in The Journal of Applied Physiology in 1980.
There could be no doubt that the experimental procedure was somehow responsible for the bubble problems that we saw. This provides a fine example of the fact that scientific measurements can sometimes change the thing they're trying to measure. We feel quite sure that this explained the Texas results also, although that study included no "control dives" without instrumentation. In any event, neither study showed that diving to any specific depth is safe during pregnancy whether anyone meddles with the fetus or not.
A very important reason for caution has to do with the arrangement of blood circulation in the fetus. The big difference from the adult is that the fetus does not yet use its lungs, so little blood goes to them. Uptake of oxygen and removal of excess C02 takes place in the placenta instead of the lungs.
In adult animals and humans, the lungs not only take care of gas exchange with the environment but also serve as a "full-flow filter" for the blood, removing bubbles and Ietting them disappear harmlessly. In the fetus, most of the blood bypasses the lungs through the foramen ovale or the ductus arteriosus, channels which normally close when the baby is born and the lungs start functioning. In the fetus, without filtration in the lungs, bubbles that form for any reason whatsoever can circulate freely and may lodge in some vital organ such as the brain or heart muscle. In some adult humans, the foramen or the ductus has failed to close normally; and these individuals are at unusual risk much like thc fetus, from bubbles that form following a dive.
We once thought that bubble formation isn't as likely to occur in the fetus as in the mother -- so that the fetus might be all right even if the mother developed decompression sickness. In a study that we conducted at Wisconsin for another purpose, we made simulated dives repeatedly with a lot of sheep. All of them had mild bends on at least two occasions. Some of the ewes became pregnant during the study, and most of them delivered nice, normal lambs. But the number of stillbirths was much higher than normal, and all of these fetal deaths followed a "bends event" in the mother. No lambs were born alive to mothers who had decompression sickness following the last dive before delivery.
Going back to the Undersea Medical Society workshop in 1978, one of the most constructive participants was a young nurse from Florida, Margie Bolton. She was in the midst of conducting a questionnaire survey of women divers who had been pregnant. When the results of her study came out in 1980, the most alarming finding was that 5.5 percent of babies born to mothers who had continued diving during pregnancy had birth defects against none in those whose mothers had stopped diving.
Five percent is not far from the overall national average for birth defects in general; and surveys like Margie's are open to a lot of questions. Nevertheless, there is reason for a lot of concern about the possibility of causing developmenal defects tha would arise very early --perhaps even before a woman realized that she was pregnant. Margie Bolton came to the University of Wisconsin to work on a Ph.D. in physiology under Dr. John Rankin. Among other things, she conducted a study involving 40 pregnant ewes, half of which made repeated dry dives during the crucial 12-40 day period when most development of parts and organs takes place in the sheep fetus. Margie found few birth defects, and there was no significant difference between "dived" and "non-dived" animals in that respect.
While the report of her sheep study was still "in press" in a leading obstetrical journal, Margie was hurt in an accident that involved severe head injury. She has not been able to conduct any further research. A number of additional studies have been conducted by others, but whatever anyone can show in animals, it is not safe to apply the conclusions direcly to human divers.
No one is likely to conduct the sort of study that might really answer the question: to have two evenly-matched groups of female divers of child-bearing age and to encourage one group to dive during pregnancy and to ensure that the other group did not do so. From the ethical standpoint, such a study would be indefensible no matter what it showed or how important it seemed at the time.
Then what advice can we give to a diver who is or may be pregnant? All I can say now in good conscience is to stop diving if you are or may be pregnant. If you intend to become pregnant, please stop diving first. These are hard words, and surely some depths and times and kinds of diving must be all right. The problem is that no one can yet be sure what would be safe and what wouldn't. (And of course, decompression isn't the only factor in diving that might harm a fetus - or the mother.) The only thing I'm sure about now is that - until a lot more experience accumulates and gets analyzed -- anybody who tells you that such-and-such limits are safe for pregnant divers is guessing -- and may very well be guessing wrong.
