There are a number of different types of decelerations, each with varying significance. This reduction in heart rate to reduce myocardial demand is referred to as a deceleration. Unlike an adult, a fetus cannot increase its respiration depth and rate. In response to hypoxic stress, the fetus reduces its heart rate to preserve myocardial oxygenation and perfusion. The fetal heart rate is controlled by the autonomic and somatic nervous system. CTG: Accelerations Decelerationsĭecelerations are an abrupt decrease in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds. The absence of accelerations with an otherwise normal CTG is of uncertain significance. The presence of accelerations is reassuring.Īccelerations occurring alongside uterine contractions is a sign of a healthy fetus. Prematurity: variability is reduced at earlier gestation (Drugs: opiates, benzodiazepines, methyldopa and magnesium sulphate.Fetal acidosis (due to hypoxia): more likely if late decelerations are also present.Fetal sleeping: this should last no longer than 40 minutes (this is the most common cause).Reduced variability can be caused by any of the following: 2 more than 25 bpm for more than 25 minutes.less than 5 bpm for more than 50 minutes.less than 5 bpm for between 30-50 minutes.Variability can be categorised as either reassuring, non-reassuring or abnormal. To calculate variability you need to assess how much the peaks and troughs of the heart rate deviate from the baseline rate (in bpm). Normal variability indicates an intact neurological system in the fetus. It is, therefore, a good indicator of how healthy a fetus is at that particular moment in time, as a healthy fetus will constantly be adapting its heart rate in response to changes in its environment. Variability occurs as a result of the interaction between the nervous system, chemoreceptors, baroreceptors and cardiac responsiveness. Severe prolonged bradycardia (less than 80 bpm for more than 3 minutes) indicates severe hypoxia.Ĭauses of prolonged severe bradycardia include:īaseline variability refers to the variation of fetal heart rate from one beat to the next. Occiput posterior or transverse presentations.It is common to have a baseline heart rate of between 100-120 bpm in the following situations: CTG: Baseline heart rate Fetal tachycardiaįetal tachycardia is defined as a baseline heart rate greater than 160 bpm.įetal bradycardia is defined as a baseline heart rate of less than 110 bpm. Look at the CTG and assess what the average heart rate has been over the last 10 minutes, ignoring any accelerations or decelerations.Ī normal fetal heart rate is between 110-160 bpm. The baseline rate is the average heart rate of the fetus within a 10-minute window. Uterine contractions (CTG) Baseline rate of the fetal heart In the below example, there are 2 contractions in a 10 minute period (this is often referred to as “2 in 10”).Intensity: How strong are the contractions (assessed using palpation)?.Duration: How long do the contractions last?.Individual contractions are seen as peaks on the part of the CTG monitoring uterine activity. Next, you need to record the number of contractions present in a 10 minute period.Įach big square on the example CTG chart below is equal to one minute, so look at how many contractions occurred within 10 big squares. Oxytocin induction/augmentation of labour.Some reasons a pregnancy may be considered high risk are shown below. if the pregnancy categorised as high-risk, the threshold for intervention may be lower). This is important as it gives more context to the CTG reading (e.g. When performing CTG interpretation, you first need to determine if the pregnancy is high or low risk. The most popular structure can be remembered using the acronym DR C BRAVADO: To interpret a CTG you need a structured method of assessing its various characteristics. The CTG is then assessed by a midwife and the obstetric medical team. One transducer records the fetal heart rate using ultrasound and the other transducer monitors the contractions of the uterus by measuring the tension of the maternal abdominal wall (providing an indirect indication of intrauterine pressure). It involves the placement of two transducers onto the abdomen of a pregnant woman. The device used in cardiotocography is known as a cardiotocograph. You might also be interested in our premium collection of 1,000+ ready-made OSCE Stations, including a range of CTG interpretation stations ✨ How CTG works
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