Pregnancy is not a relative contraindication to hyperbaric oxygen treatments, although it may be for underwater diving. In cases where a pregnant woman has carbon monoxide poisoning there is evidence that lower pressure (2.0 ATA) HBOT treatments are not harmful to the fetus, and that the risk involved is outweighed by the greater risk of the untreated effects of CO on the fetus (neurologic abnormalities or death.) In pregnant patients, HBO therapy has been shown to be safe for the fetus when given at appropriate levels and “doses” (durations). In fact, pregnancy lowers the threshold for HBO treatment of carbon monoxide-exposed patients. This is due to the high affinity of fetal hemoglobin for CO.