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Chapter 8 — 8
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Decompression sickness.
As mentioned earlier, women may have increased susceptibility to DCS and there are
theoretical reasons to believe that pregnant women are even more susceptible. It is known from
Doppler studies that showers of bubbles are regularly formed in the veins of divers ascending
from many routine non-decompression dives. These bubbles do not usually cause any
symptoms.
Some experiments in pregnant animals suggest that the foetus is more resistant to bubble
formation than the mother but that bubbles do form after some dives, especially those deeper
than 20 metres. Because of the unique circulation of the foetus even a few bubbles in the foetal
circulation can have disastrous consequences.
Experiments with pregnant animals have produced conflicting results. One study on pregnant
sheep (which have a placenta similar to a human) showed that the foetus developed bubbles in
its circulation even after dives of less than 30 metres (100 ft.) and within the US Navy no-
decompression limits. These results are disturbing when considering the vulnerability of the
foetus to any bubble.
Other studies have shown an increased incidence of abortion, birth defects and still-births in
pregnant animals after decompression.
Exposure to hyperbaric oxygen has also been shown in some studies to cause birth
abnormalities and death.
Human Data
Japanese female divers, the Ama, often dived until late pregnancy, and had a 44% incidence of
premature delivery with a high incidence of small babies when compared with non-diving
women from the same area. Another survey on modern day Ama, who were not exposed to the
same stresses, did not reflect this association.
Margaret Bolton from the University of Florida carried out a survey on 208 women who dived
during pregnancy. She found an increased incidence of abortion, still-birth, low birth weight
and death of the infant within the first month. Of the 24 women who reported diving to 30
metres (100 ft) or more, three had children with congenital defects. This contrasts with an
incidence of 1 in 50 in the general population. One of the infants had an absent hand, a very
rare abnormality.
An Australian case report, showing multiple grotesque abnormalities after diving, suggested
that the effects and vulnerable time frame may be similar to taking congenital-abnormality
producing drug, Thalidomide, during pregnancy.
It is difficult to draw firm conclusions from these studies, or others that have been conducted,
because the numbers are too low for statistical validation, or are retrospective. They are
however consistent with many of the animal studies.
The Bottom Line ---
There is considerable evidence suggesting that diving during pregnancy is harmful to the
foetus. It is generally accepted that unnecessary drugs, alcohol and smoking should be avoided
during pregnancy because of the risk to the foetus and we recommend a similar conservative