During pregnancy, monitoring the well-being of the developing baby is a common practice. One frequently used method for this assessment is the Nonstress Test, often referred to as an NST. This non-invasive procedure provides valuable insights into the baby’s condition.
What is a Nonstress Test?
A Nonstress Test is a prenatal screening that measures a baby’s heart rate in response to its movements. It is called “nonstress” because it places no physical stress on the pregnant individual or the fetus. The primary purpose of an NST is to assess the baby’s overall health and confirm adequate oxygen supply. This test relies on the observation that a healthy baby’s heart rate temporarily increases with movement. NSTs are typically performed after 28 weeks of pregnancy, when the fetal heart rate begins to consistently react to movements.
Reasons for an NST
Healthcare providers may recommend an NST for various medical reasons. It is often performed if a pregnancy extends beyond its due date, usually past 40 weeks. An NST is also a common recommendation for individuals with high-risk pregnancies, such as those with chronic conditions like gestational diabetes, high blood pressure, or heart disease. Other indications include a noticeable decrease in fetal movement, concerns about fetal growth, or a history of complications in previous pregnancies. It may also be used in cases of Rh incompatibility or if carrying multiple babies, especially with associated complications.
The NST Procedure
The Nonstress Test is a simple procedure typically conducted in a doctor’s office or a hospital’s prenatal area. The pregnant individual lies comfortably in a reclined position, and two elastic belts with sensors are placed around the abdomen. One sensor monitors the baby’s heart rate, which can often be heard, while the other tracks uterine contractions, even those that may not be felt. The test usually lasts between 20 to 30 minutes, though it can extend up to 40 minutes if the baby is inactive. If the baby is quiet or asleep, the healthcare provider may use a gentle buzzing device on the abdomen or suggest drinking a sugary beverage to encourage movement.
Understanding and Responding to NST Results
Results from a Nonstress Test are typically categorized as either “reactive” or “nonreactive.” A “reactive” result is reassuring, indicating that the baby’s heart rate increased at least twice during the test in response to movement. This acceleration means the heart rate rises by 15 beats per minute above the baseline for at least 15 seconds, occurring within a 20-minute period. This pattern suggests the baby is well-oxygenated and healthy.
A “nonreactive” result occurs when the fetal heart rate does not show these expected accelerations. This outcome does not automatically signal a problem; often, it means the baby was simply asleep during the test or that certain medications affected its activity. In such cases, further evaluation is usually recommended to gather more information about the baby’s condition. Additional tests might include a biophysical profile, which combines an ultrasound with an NST, or a contraction stress test, which assesses the baby’s response to mild contractions.