function calculatePregnancyTest() {
var ovulationDateStr = document.getElementById("ovulationDate").value;
var testDateStr = document.getElementById("testDate").value;
var testSensitivity = parseFloat(document.getElementById("testSensitivity").value);
var implantationDay = parseInt(document.getElementById("implantationDay").value);
var resultDiv = document.getElementById("result");
if (!ovulationDateStr || !testDateStr || isNaN(testSensitivity) || isNaN(implantationDay)) {
resultDiv.innerHTML = "Please fill in all fields with valid numbers and dates.";
resultDiv.style.backgroundColor = '#f8d7da';
resultDiv.style.borderColor = '#f5c6cb';
resultDiv.style.color = '#721c24';
return;
}
var ovulationDate = new Date(ovulationDateStr);
var testDate = new Date(testDateStr);
// Reset time components to avoid issues with timezones/daylight saving
ovulationDate.setHours(0, 0, 0, 0);
testDate.setHours(0, 0, 0, 0);
if (testDate < ovulationDate) {
resultDiv.innerHTML = "The test date cannot be before the ovulation date. Please check your dates.";
resultDiv.style.backgroundColor = '#f8d7da';
resultDiv.style.borderColor = '#f5c6cb';
resultDiv.style.color = '#721c24';
return;
}
var timeDiff = testDate.getTime() – ovulationDate.getTime();
var daysPastOvulation = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
var daysPastImplantation = daysPastOvulation – implantationDay;
var estimatedHCG = 0;
var message = "";
var bgColor = '#e9f7ef';
var borderColor = '#d4edda';
var textColor = '#155724';
if (daysPastImplantation = testSensitivity) {
message = "Based on your inputs, your estimated hCG level on the test date is approximately " + estimatedHCG.toFixed(1) + " mIU/mL. Given your test sensitivity of " + testSensitivity + " mIU/mL, a positive result is likely.";
} else {
message = "Based on your inputs, your estimated hCG level on the test date is approximately " + estimatedHCG.toFixed(1) + " mIU/mL. This is below your test's sensitivity of " + testSensitivity + " mIU/mL. A negative result is likely, but it might still be too early. Consider retesting in 2-3 days.";
bgColor = '#fff3cd';
borderColor = '#ffeeba';
textColor = '#856404';
}
}
resultDiv.innerHTML = message;
resultDiv.style.backgroundColor = bgColor;
resultDiv.style.borderColor = borderColor;
resultDiv.style.color = textColor;
}
Understanding Early Pregnancy Tests and hCG
Early pregnancy tests work by detecting the presence of human chorionic gonadotropin (hCG) in your urine. hCG is a hormone produced by the cells that will eventually form the placenta. It's often referred to as the "pregnancy hormone" because it's only present in your body when you're pregnant.
When Does hCG Appear?
hCG begins to be produced shortly after a fertilized egg implants into the uterine wall. Implantation typically occurs between 6 to 12 days past ovulation (DPO), with the most common range being 8 to 10 DPO. Once implantation occurs, hCG levels start to rise rapidly.
How Fast Do hCG Levels Rise?
In early pregnancy, hCG levels usually double approximately every 48 to 72 hours (2 to 3 days). This rapid increase is what allows pregnancy tests to become positive as pregnancy progresses.
Test Sensitivity Explained
Not all pregnancy tests are created equal. They vary in their "sensitivity," which is measured in milli-international units per milliliter (mIU/mL). This number indicates the minimum concentration of hCG the test can detect to show a positive result:
Highly Sensitive Tests (e.g., 10-20 mIU/mL): These tests can detect lower levels of hCG, meaning they can potentially give a positive result earlier in pregnancy.
Standard Tests (e.g., 25-50 mIU/mL): These require a higher concentration of hCG and might not show a positive result until a few days after a highly sensitive test would.
The calculator above helps you estimate your hCG level based on your ovulation and test dates, and compares it to your test's sensitivity to predict the likelihood of a positive result.
Interpreting Your Results
Likely Positive: If your estimated hCG level is above your test's sensitivity, a positive result is expected.
Likely Negative (but possibly too early): If your estimated hCG level is below the test's sensitivity, the test might show negative. This doesn't necessarily mean you're not pregnant; it could just mean your hCG levels aren't high enough for that specific test to detect yet. In this case, it's often recommended to retest in 2-3 days, as hCG levels will have significantly increased if you are pregnant.
Too Early for Implantation: If the calculator indicates it's too early for implantation, any test would be negative. Wait until after your estimated implantation day to test.
Remember, this calculator provides an estimate. For definitive results, always follow up with a healthcare professional.