– Should I Dive Whilst Pregnant?
by Marguerite St Leger Dowse
There will always be women who dive not knowing they are pregnant, or deliberately choose to dive whilst pregnant. With most medical recommendations concerning women in recreational diving based on the physiology of fit young men and animals, how do we determine safe limits to dive whilst pregnant?
Research has centred on the foetal/unborn child’s susceptibility to decompression illness (DCI), safe limits to dive, and foetal abnormalities. The foetal circulation differs from the adult where almost all the output from the heart travels through the lungs where small bubbles are removed. Foetal circulation bypasses the foetal lungs. Any bubble that develops via the foetal tissue or the placental tissue will travel through the foetal foramen ovale into the foetal arterial circulation and embolise to the developing tissues of the foetus, possibly causing damage to these tissues. If this occurs in sensitive areas such as the nervous system of the unborn child there could be significant consequences.
Human research Between 1978 and 1989 a flurry of human retrospective questionnaire studies attempted to establish a link between diving and foetal abnormalities. Bangasser’s (1978 USA) study found no abnormalities in her survey of 72 diving respondents, although she speculated that diving may cause complications, and sited spontaneous abortion as a factor.
Two years later Bolton (1980, USA) published a study of 208 respondents. 136 women had dived whilst pregnant, reporting 145 dived pregnancies. She found there were more foetal abnormalities in diving mothers (5.5%) compared with the non diving group (0.0%) within her study. However, the study percentage of 5.5% was within the expected range for the general USA population as a whole. Thus no firm conclusions were drawn.
She concluded that it is the lack of definitive evidence that warrants concern for foetal well-being.
This study has remained the most quoted work in this field.
In 1985 Betts (UK) and 1989 Bakkevig (Scandinavia) published two separate studies which included 76 and 34 dived pregnancies respectively. The number of respondents in both surveys was too small to be statistically significant, but both observed an incidence of foetal abnormalities in the reported dived pregnancies, recommending women who dive whilst pregnant to limit their diving to shallow depths.
All these studies were retrospective, and questionnaire based, increasing the probability that respondents with a problem were more likely to respond; thus potentially influencing the results.
In 2006 the Diseases Research Centre (DDRC) in the UK published data from two unrelated field studies – the men and women study (M&W) and the menstrual cycle study (MC). 129 women had reported having dived whilst pregnant with 157 pregnancies over 1,465 dives. In the earlier M&W study 65% of women stopped diving in the first three months, with respondents reporting 12 pregnancies where the first dive had been made in the second three months, and 35 weeks being the latest time of diving during pregnancy. By comparison, by the later MC study more than 90% of women ceased diving in the first three months of their pregnancy, with 26 weeks reported as the latest time in the pregnancy of diving. Compare this with the much earlier famous Bolton study (1980) where 20% of women were still diving in the final three months of the pregnancy.
Altogether, of the 157 pregnancies that failed for various reasons, the spontaneous abortion rate in the study group of diving women was no different than the upper limit of the rate in the general UK population. Of the live births, 80% were seen by the respondents as problem free, with the remaining 20% of women reporting a variety of perceived problems with the pregnancy or outcome. But remember the underlying factors, with regard to the lifestyles and activities of a typical female recreational diver. Some women were horse-back riding, sky-diving, taking recreational drugs, and generally getting on with their lives, so you would expect some problems!
Research studies, as we all know, are about numbers and overall the women in the DDRC study (as with the other studies) did not conduct enough dives per pregnancy to demonstrate any significant link between pregnancy outcome and safe limits to dive. For significant results to be meaningful more than 4,000 women would need to have a relevant exposure to diving whilst pregnant. The problem is that women are increasingly observing the diving industry recommendation – which is not to dive whilst pregnant. So, researchers are faced with the following conundrum: because of the recommendations it means that less women are diving whilst pregnant. There are therefore less dives per pregnancy, and thus less data for researchers to study!
So what about animal studies? Many animal studies were conducted up to the late 1980’s, and may not be an appropriate model on which to base recommendations for humans. This is partly due to differences in placental circulation. To this day animal studies remain controversial and inconclusive.
What next? The debate over the years has focused on foetal abnormalities and depth dived. However, in the DDRC study many of the pregnant women were diving across all categories of depths and reported no problems with the pregnancy or the outcome. This does not imply though that diving is safe whilst pregnant, but neither is it possible to recommend or establish safe limits within which to dive.
Given the decreasing number of women diving whilst pregnant, and the limitations of animal research, a definitive answer is likely to remain elusive. However, the data the industry has at its disposal emphasises that women who have dived whilst pregnant need not be encouraged to terminate their pregnancy. But the author Maida Beth Taylor sums it up succinctly, “…..The short term pleasure of diving must be balanced against the potential long-term effects on the foetus as a passive passenger at depth.”
So, the take home message remains: If you trying to become pregnant or are already pregnant and want to be sure that any problem with the pregnancy and/or outcome cannot be attributed to diving, then don’t dive.
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Book: Women and Pressure