The question of whether it is safe to scuba dive during pregnancy is common among avid divers. Scuba diving introduces unique physiological stressors and changes in ambient pressure that pose a potential hazard to the developing fetus. Since ethical restrictions prevent controlled studies on pregnant human divers, medical and diving organizations advise extreme caution. Understanding the physics of gas exchange under pressure and the distinct nature of fetal circulation clarifies why this activity carries a substantial, though not fully quantifiable, risk to the unborn child.
Why Scuba Diving is Contraindicated During Pregnancy
Medical and professional diving organizations, including the Divers Alert Network (DAN) and the American College of Obstetricians and Gynecologists (ACOG), advise against scuba diving throughout the entire gestation period. This recommendation is based on precautionary principles, given the limited human data available. The primary concern is the potential for fetal injury from decompression stress, which may occur even if the pregnant individual appears asymptomatic.
The core issue stems from the transfer of inert gases, primarily nitrogen, from the mother’s bloodstream to the fetus. Scuba diving requires the body to absorb a higher concentration of nitrogen gas under increased pressure. While the effects of this absorption and subsequent decompression on the mother are well-documented, the impact on the fetal environment is not fully understood. Avoidance of diving is the universal instruction from medical professionals and dive training agencies.
The Risk of Fetal Decompression Sickness
Decompression sickness (DCS) occurs when dissolved inert gases, absorbed under pressure, form bubbles in the body’s tissues and circulation upon ascent. During a dive, nitrogen gas travels from the mother’s blood across the placenta into the fetal circulation. The fetus absorbs and accumulates nitrogen, dependent on the depth and duration of the dive. The risk of bubble formation upon ascent is magnified in the fetus due to its unique circulatory system.
In a healthy adult diver, small nitrogen bubbles that form in the venous blood are typically filtered out and eliminated by the lungs. The fetal circulatory system, however, is designed to bypass the non-functional lungs. Two specialized structures, the foramen ovale and the ductus arteriosus, allow blood to shunt away from the fetal lungs. These shunts are open during gestation because the fetus receives oxygenated blood from the placenta.
During decompression, if nitrogen bubbles form in the fetal venous blood, these circulatory shunts can allow them to pass directly into the arterial circulation. Since the fetal lungs are bypassed, they cannot filter the bubbles as the mother’s lungs would. This phenomenon, known as paradoxical gas embolism, can send bubbles to sensitive tissues, including the brain and spinal cord. This results in severe fetal DCS or arterial gas embolism. Animal studies have demonstrated that fetal DCS can occur even when the mother shows no signs of decompression illness.
These studies have linked hyperbaric exposure to adverse outcomes such as fetal death, low birth weight, and developmental abnormalities, including defects in the skull and limbs. Although the applicability of animal data to humans has limits, the mechanism of bubble formation and the presence of the fetal shunts represent a clear danger to the unborn child.
Other Maternal and Fetal Physiological Concerns
Beyond the risks associated with nitrogen saturation and bubble formation, pregnancy introduces several physiological changes that complicate the diving environment. Fluid retention can cause swelling of the mucous membranes in the nasal passages and sinuses. This swelling makes pressure equalization more difficult, increasing the risk of painful ear or sinus barotrauma. The growing abdomen alters the pregnant individual’s center of gravity and flexibility, making managing heavy scuba gear and performing water entries and exits more challenging.
Ill-fitting equipment, such as a snug wetsuit or an improperly positioned buoyancy compensation device (BCD), can cause discomfort or restrict blood flow. Increased fatigue and potential morning sickness, exacerbated by motion on a dive boat, introduce additional safety hazards. Vomiting underwater could lead to regulator loss and a panic ascent. Physical exertion or exposure to cold water can also contribute to maternal dehydration or thermal stress.
Another concern relates to maternal blood pressure regulation during a dive, particularly during ascent or while carrying heavy equipment. Maternal hypotension, or low blood pressure, can reduce blood flow through the placenta, potentially decreasing oxygen delivery to the fetus. The diving environment adds a layer of unpredictable risk to this delicate circulatory balance.
Safe Water Activities and Alternatives
For individuals who enjoy being in the water, several safe and beneficial activities can replace scuba diving during pregnancy. Swimming is widely recommended as one of the safest forms of exercise, as water buoyancy relieves pressure on joints and the back. Water aerobics and walking in a pool offer similar benefits, helping to maintain fitness without the risk of falling or excessive impact. Snorkeling is a permissible alternative, provided the activity remains strictly surface-based without breath-hold diving. It is important to avoid any activity that involves breath-holding, as this can temporarily reduce oxygen supply to the fetus.