Pulse oximetry screening, often referred to as “pre and post-ductal sats,” is a routine and non-invasive health check performed on newborns. This simple test helps medical professionals quickly assess a baby’s oxygen levels in the blood. Its primary purpose is to identify potential underlying health concerns, particularly those related to the heart, before a baby leaves the hospital. This screening serves as an important measure in comprehensive newborn care.
Understanding Oxygen Saturation and Ductal Flow
Oxygen saturation, or “sats,” refers to the percentage of hemoglobin in the blood that is carrying oxygen. It indicates how effectively the body is distributing oxygen to its tissues and organs. Higher saturation levels generally mean more oxygen is available for the body’s needs.
Before birth, a baby’s circulatory system operates differently from how it does after birth. The fetal heart has a special blood vessel called the ductus arteriosus. This vessel allows blood to bypass the lungs, as the baby receives oxygen directly from the mother’s placenta. It shunts blood from the pulmonary artery directly into the aorta, distributing oxygenated blood to the body.
Upon birth, as the newborn takes its first breaths, the lungs inflate. The pulmonary vascular resistance decreases, allowing blood to flow to the lungs for oxygenation. The ductus arteriosus typically begins to constrict and functionally close within the first 12 to 24 hours of life in healthy, full-term newborns. Measuring oxygen levels before (pre-ductal) and after (post-ductal) this vessel’s influence helps detect differences in oxygen delivery, which could indicate a heart issue.
The Screening Process: Limb Placement and Measurement
The “pre and post-ductal sats” screening specifically involves measurements from two distinct locations on the baby’s body. The pre-ductal oxygen saturation is obtained from the baby’s right hand or arm. This limb is chosen because the blood flowing to the right arm branches off the aorta before the ductus arteriosus. This represents oxygen levels in blood that has not yet been influenced by any shunting through the ductus.
The post-ductal measurement is taken from either leg or foot. Blood reaching the legs has traveled through the descending aorta, which is located after the point where the ductus arteriosus connects. Therefore, a comparison between the right hand and a foot can reveal if there is a significant difference in oxygen levels. This could potentially indicate abnormal blood flow through a still-open or improperly closing ductus arteriosus.
The measurement method used for this screening is pulse oximetry. A small, soft sensor, often an adhesive strip, is gently placed around the baby’s right hand and one foot. This device shines a light through the skin and measures how much oxygen is carried by the blood, displaying the oxygen saturation as a percentage. The test is quick, painless, and non-invasive for the newborn. This screening is usually performed when the baby is at least 24 hours old, but often before hospital discharge. This ensures the circulatory system has transitioned adequately from fetal to newborn circulation.
Interpreting Newborn Screening Results
A “passing” result for the pulse oximetry screening indicates healthy oxygen levels in the newborn’s blood. Generally, a screen is considered passed when the oxygen saturation measure is 95% or higher in both the right hand and the foot. Additionally, the absolute difference in oxygen saturation between the right hand and the foot should be 3% or less.
An “abnormal” or “failed” screen occurs under specific criteria:
Any oxygen saturation reading below 90% in either the right hand or the foot.
Oxygen saturation below 95% in either the right hand or foot on two separate measurements.
A difference in oxygen saturation greater than 3% between the right hand and the foot on two measurements.
An abnormal screen does not automatically mean a baby has a heart defect. Other factors, such as lung problems or infections, can also lead to lower oxygen levels. When an abnormal result occurs, further evaluation is necessary. This might include:
A repeat screening.
A thorough physical examination.
Additional medical assessments like an echocardiogram, an ultrasound of the heart.
The Importance of Early Detection
The widespread implementation of pre and post-ductal oxygen saturation screening is a significant advancement in newborn care. This simple test helps identify critical congenital heart disease (CCHD) early, often before any symptoms become apparent. Many infants with CCHD may appear healthy at birth, and their heart conditions might otherwise go undetected until they become severely ill, sometimes after hospital discharge.
Early detection through this screening allows for timely medical intervention. This can significantly improve a baby’s health outcomes and prevent serious complications. Identifying these conditions early can lead to life-saving treatments, ranging from medication and close monitoring to surgical procedures, often performed within the first days or weeks of life. This non-invasive screening plays a crucial role in safeguarding the health of newborns, ensuring they receive the necessary medical attention if a potential issue is identified.