Oxygen saturation (SpO2) measures the percentage of oxygen carried by red blood cells throughout the body. This value indicates how much hemoglobin, the protein responsible for oxygen transport, is currently bound to oxygen. Monitoring SpO2 is a standard procedure in modern newborn care immediately after birth and during the hospital stay. A stable oxygen saturation level confirms that a newborn’s lungs and heart are effectively delivering the necessary oxygen for healthy development.
Understanding Pulse Oximetry
A pulse oximeter measures a newborn’s oxygen levels non-invasively. This small device uses a sensor, typically a soft, adhesive wrap or clip, placed on a part of the baby’s body with good blood flow, such as a foot or the right hand. The right hand measurement provides a reading of oxygenated blood circulating before it mixes with blood from the fetal circulation pathways.
The oximeter operates by emitting red and infrared light through the tissue. Hemoglobin absorbs these light wavelengths differently depending on whether it is carrying oxygen. By measuring how much light is absorbed by the blood pulsing through the capillaries, the device rapidly calculates the percentage of oxygen-saturated hemoglobin. This technology provides continuous, painless data to medical staff about the baby’s cardiopulmonary function.
This test is also the basis for the newborn screening program to detect Critical Congenital Heart Disease (CCHD) before hospital discharge. The screening identifies heart defects that can cause dangerously low oxygen levels, even when a baby appears healthy. Early detection allows for prompt medical intervention, which improves outcomes for infants with these conditions.
Target Oxygen Levels for Newborns
A newborn’s oxygen saturation level changes significantly during the first minutes of life as the baby transitions from relying on the placenta to using their own lungs. Immediately following birth, a healthy term newborn’s SpO2 is naturally low, often ranging from 60% to 80%. This is expected because the lungs are just beginning the process of full oxygen exchange.
This initial oxygen level rises gradually over the first ten minutes during the transitional phase. Studies show that the median SpO2 reaches approximately 66% at one minute and 73% at two minutes post-delivery. By the five-minute mark, the median saturation typically reaches 89%. It takes a median of about eight minutes for a healthy newborn to consistently register an SpO2 value above 90%.
Once a baby stabilizes, usually within the first few hours or days of life, the target saturation range shifts higher. For a full-term, stable newborn breathing room air, the expected oxygen saturation range is 95% to 100%. Readings consistently below 95% suggest the baby may need further evaluation. A reading that persists below 90% is a threshold that prompts immediate medical concern and intervention.
Common Reasons for Low Readings
When a newborn’s SpO2 dips below the stable target of 95%, the cause may relate to the lungs, heart, or blood circulation. Respiratory Distress Syndrome (RDS) is a frequent reason, particularly in premature infants whose lungs lack the necessary surfactant to keep air sacs open. Transient Tachypnea of the Newborn (TTN) is a temporary condition often seen after C-sections, where fetal lung fluid is not cleared quickly enough, leading to rapid, shallow breathing and lower saturation.
Another pulmonary factor is Aspiration, which occurs when a baby inhales foreign material, such as meconium (the first stool), into the lungs before or during birth. This material can block airways and cause inflammation, impairing oxygen absorption. Infections, such as sepsis, can also stress the baby’s system, including the lungs, leading to a drop in oxygen levels.
Structural problems with the heart, known as Congenital Heart Defects (CHD) or Critical Congenital Heart Disease (CCHD), are non-respiratory causes of low SpO2. Certain defects cause a right-to-left shunt, meaning deoxygenated blood bypasses the lungs and is pumped directly into the body’s circulation, resulting in lower saturation. Non-medical factors can also temporarily impact a reading, such as excessive crying, shivering, or an improperly placed sensor that cannot get a strong signal.
Recognizing a Medical Emergency
Parents and caregivers monitoring a newborn outside the hospital should be aware of visible signs indicating a dangerous drop in oxygen levels, even without a pulse oximeter. The primary visual indicator is cyanosis, a bluish or dusky discoloration of the skin, especially around the lips, tongue, and nail beds. While a baby’s hands and feet may appear blue when cold, blueness of the central body or mucous membranes is a serious warning sign.
Signs of difficulty breathing are clear indicators of low oxygen. These include nasal flaring, where the nostrils widen with each breath, and a noticeable increase in the speed and effort of breathing. Parents may also observe retractions, a sucking-in motion of the skin between the ribs or beneath the breastbone as the baby struggles to pull air into the lungs.
A change in a newborn’s behavior suggests a medical emergency. This includes profound lethargy, where the baby is unusually difficult to wake or keep awake, or a lack of responsiveness to stimulation. If a baby exhibits any of these signs—central blueness, labored breathing, or severe unresponsiveness—emergency medical services or a pediatrician should be contacted immediately for evaluation.