Oxygen saturation (SpO2) measures the percentage of hemoglobin in the blood carrying oxygen. This reading provides a quick, non-invasive assessment of how effectively the lungs deliver oxygen to the body. Like heart rate and blood pressure, SpO2 is a fundamental sign of overall health and respiratory function. Maintaining adequate oxygen delivery is crucial during pregnancy because the supply must support both the mother’s metabolism and the developing fetus. Understanding normal readings and when a reading is concerning provides important perspective on maternal well-being.
Defining Normal Oxygen Levels During Pregnancy
The expected oxygen saturation range for a healthy pregnant person at sea level is typically between 95% and 100%. While similar to non-pregnant adults, the respiratory system achieves this stability through significant physiological adaptations. Oxygen demand increases substantially during pregnancy to meet the metabolic needs of the fetus, placenta, and maternal tissues.
To compensate, hormonal changes, particularly a rise in progesterone, act as a respiratory stimulant. This causes a slight but persistent increase in the rate and depth of breathing, known as physiological hyperventilation. This results in a greater volume of air inhaled and exhaled, which helps maintain high blood oxygen levels.
Although the SpO2 number remains high, the pregnant person’s body operates with less reserve than a non-pregnant person. Even with moderate exertion during the second and third trimesters, a healthy person’s oxygen saturation should not fall below 95%. A sustained reading below this threshold warrants prompt attention.
How Oxygen Saturation is Measured
Oxygen saturation is most commonly measured using a device called a pulse oximeter, which painlessly clips onto a finger, toe, or earlobe. This small device works by emitting two wavelengths of light—red and infrared—through the tissue. It measures how much light is absorbed by the blood, as oxygenated and deoxygenated hemoglobin absorb light differently.
The device uses this information to calculate the percentage of hemoglobin carrying oxygen, displaying the result as the SpO2 reading. While convenient, home-use pulse oximeters can sometimes produce inaccurate or misleading results. Several factors can interfere with the reading:
- Movement during the reading, such as trembling or fidgeting, can disrupt the sensor’s ability to detect a consistent blood flow.
- Poor peripheral circulation, often caused by cold extremities, can lead to falsely low readings because there is insufficient blood flow for the light to measure effectively.
- External factors like dark nail polish or artificial nails can interfere with the light absorption, potentially causing an underestimation of the true saturation level.
- Differences in skin pigmentation have been shown to affect accuracy, with some devices having a tendency to overestimate the saturation in individuals with darker skin tones.
Recognizing Symptoms of Low Oxygen
A drop in maternal oxygen levels, known as hypoxemia, can be a serious medical concern as it risks insufficient oxygen delivery to the fetus. Symptoms a pregnant person might experience if their SpO2 is dipping include noticeable shortness of breath that is severe or suddenly worsens. Other signs can involve a rapid heart rate, confusion, or a feeling of being unusually listless and tired.
In more severe cases, a bluish discoloration of the skin, lips, or nail beds, medically termed cyanosis, indicates a dangerous lack of oxygen. This state of maternal hypoxia is particularly concerning because the fetus is completely dependent on the mother’s blood oxygen supply. A sustained drop in the mother’s oxygen can restrict the blood flow to the placenta, jeopardizing the fetus’s oxygenation.
Maternal hypoxia can lead to a condition in the fetus called Hypoxic-Ischemic Encephalopathy (HIE), which is brain injury resulting from a lack of oxygen and blood flow. This lack of oxygen carries the potential for serious complications, including developmental delays and long-term neurological damage. Therefore, any pronounced or persistent symptoms of low oxygen require immediate medical evaluation to protect both the pregnant person and the developing baby.
Maintaining Healthy Oxygen Levels and Seeking Medical Help
Maintaining healthy oxygen levels involves proactive steps, especially for managing common discomforts that affect breathing during pregnancy. Proper positioning, such as lying on the left side, is a simple action that can help by relieving pressure on the major blood vessels, which improves blood flow to the uterus and, consequently, oxygen supply to the fetus. Practicing deep, controlled breathing techniques can also increase lung efficiency and improve blood oxygen levels.
Staying well-hydrated is important because dehydration can negatively impact blood circulation, which is what carries oxygen throughout the body. Ensuring adequate iron intake, often through supplements recommended by a healthcare provider, is also helpful since iron is required to produce the extra red blood cells needed to transport oxygen during pregnancy.
It is important to contact an obstetrician or seek emergency care immediately if a person experiences a sudden, severe difficulty breathing or if breathlessness does not improve after resting or changing positions. Professional guidance suggests that any pregnant person whose SpO2 reading falls below 95% should be promptly evaluated. A persistent reading below this level, or any reading below 94%, especially when accompanied by chest pain or a racing heart, warrants an urgent trip to the hospital.