Calculate the rounded baseline FHR based on NICHD guidelines.
Enter at least 2 distinct heart rate readings (BPM) observed during stable periods within a 10-minute window. Exclude accelerations and decelerations.
Calculated Baseline FHR
— BPM
*Rounded to the nearest 5 BPM per NICHD guidelines.
How to Calculate Baseline Fetal Heart Rate
Determining the baseline Fetal Heart Rate (FHR) is a fundamental skill in electronic fetal monitoring (EFM). The baseline serves as the reference point for assessing fetal status, variability, and the presence of accelerations or decelerations.
Definition: The baseline FHR is the approximate mean FHR rounded to increments of 5 beats per minute (bpm) during a 10-minute window, excluding periodic or episodic changes, periods of marked variability, and segments of baseline that differ by more than 25 bpm.
Step-by-Step Calculation Guide
To accurately calculate the baseline without automated software, follow these clinical steps used by obstetric professionals:
Select a 10-Minute Window: Identify a 10-minute segment on the Cardiotocograph (CTG) strip.
Exclude Periodic Changes: Ignore areas with accelerations (temporary increases) and decelerations (temporary decreases).
Identify Stable Segments: Look for periods where the heart rate is relatively stable. You need at least 2 minutes of identifiable baseline segments (not necessarily contiguous) within that 10-minute window.
Estimate the Mean: Determine the average rate of these stable segments.
Round to Nearest 5 BPM: Unlike standard mathematical rounding, FHR baseline is specifically rounded to the closest 5 beat increment (e.g., a mean of 133 becomes 135, a mean of 142 becomes 140).
Interpreting the Results
Once the baseline is established, it is categorized into one of three ranges:
Normal Baseline: 110 bpm to 160 bpm. This range generally indicates an intact fetal autonomic nervous system.
Bradycardia: Less than 110 bpm. While this can be associated with fetal hypoxia, it may also result from maternal positioning, hypotension, or medications.
Tachycardia: Greater than 160 bpm. Causes can include maternal fever, infection (chorioamnionitis), fetal hypoxia, or fetal anemia.
Why the "Indeterminate" Result?
If the baseline cannot be determined because there are fewer than 2 minutes of interpretable baseline in a 10-minute window, the baseline is considered "indeterminate." In such cases, the previous 10-minute window should be reviewed for determination.
function calculateBaselineFHR() {
// 1. Get elements
var s1 = document.getElementById('sample1').value;
var s2 = document.getElementById('sample2').value;
var s3 = document.getElementById('sample3').value;
var s4 = document.getElementById('sample4').value;
var s5 = document.getElementById('sample5').value;
var resultSection = document.getElementById('resultSection');
var baselineValueDisplay = document.getElementById('baselineValue');
var interpretationBox = document.getElementById('interpretationBox');
// 2. Parse values into an array, filtering out empty strings
var samples = [s1, s2, s3, s4, s5];
var validSamples = [];
for (var i = 0; i < samples.length; i++) {
if (samples[i] !== "" && !isNaN(samples[i])) {
validSamples.push(parseFloat(samples[i]));
}
}
// 3. Validation
if (validSamples.length < 1) {
alert("Please enter at least one valid heart rate reading.");
resultSection.style.display = "none";
return;
}
// 4. Calculate Average
var sum = 0;
for (var j = 0; j < validSamples.length; j++) {
sum += validSamples[j];
}
var average = sum / validSamples.length;
// 5. Round to nearest 5 BPM (NICHD Guideline)
// Formula: Divide by 5, round to nearest integer, multiply by 5.
var roundedBaseline = Math.round(average / 5) * 5;
// 6. Display Result
baselineValueDisplay.innerHTML = roundedBaseline + " BPM";
resultSection.style.display = "block";
// 7. Clinical Interpretation
var interpretationText = "";
var statusClass = "";
if (roundedBaseline < 110) {
interpretationText = "BRADYCARDIA ( 160) {
interpretationText = "TACHYCARDIA (> 160 BPM)";
statusClass = "status-danger";
} else {
interpretationText = "NORMAL RANGE (110 – 160 BPM)";
statusClass = "status-normal";
}
interpretationBox.className = "fhr-interpretation " + statusClass;
interpretationBox.innerHTML = interpretationText;
}