Emergency contraception (EC), often referred to as the "morning-after pill" or "EC pills," is a safe and effective method to prevent pregnancy after unprotected intercourse or contraceptive failure. It is important to understand that EC is not intended for regular use but as a backup measure. The effectiveness of emergency contraception can vary depending on several factors, primarily the type of method used and how soon it is taken after the event.
How Emergency Contraception Works
Different types of emergency contraception work in slightly different ways, but their primary goal is to prevent pregnancy by:
Preventing or delaying ovulation: If ovulation has not yet occurred, EC can stop the release of an egg from the ovary, thus preventing fertilization.
Thickening cervical mucus: This can make it more difficult for sperm to travel through the reproductive tract to reach an egg.
Interfering with sperm and egg transport: In some cases, it may affect the movement of sperm or the egg within the fallopian tube.
It's crucial to note that EC is generally not effective if implantation has already occurred, meaning it is not an abortifacient.
Emergency Contraception Methods and Their Effectiveness
The calculator above estimates effectiveness based on established data for common EC methods:
Levonorgestrel (LNG) Pills (e.g., Plan B, Next Choice):
These pills are most effective when taken as soon as possible after unprotected intercourse. Their effectiveness decreases as more time passes. Studies suggest that taking LNG pills within 72 hours (3 days) of unprotected sex can prevent a significant percentage of potential pregnancies. Their effectiveness may extend slightly beyond 72 hours, but at a reduced rate.
Effectiveness within 72 hours: Estimated to prevent 75-89% of pregnancies that would have occurred.
Effectiveness beyond 72 hours: Decreases with time.
Ulipristal Acetate (UPA) Pills (e.g., Ella):
UPA is a more potent progestin that is effective for a longer period. It can be taken up to 120 hours (5 days) after unprotected intercourse.
Effectiveness within 120 hours: Estimated to prevent a higher percentage of pregnancies compared to LNG, particularly when taken later within the 5-day window.
Copper Intrauterine Device (IUD):
The Copper IUD is the most effective form of emergency contraception and can be inserted by a healthcare provider up to 120 hours (5 days) after unprotected intercourse. It also provides long-term contraception.
Effectiveness: Over 99% effective in preventing pregnancy.
How the Calculator Works
This calculator uses simplified, generalized effectiveness rates based on scientific literature. It takes into account:
Time Elapsed: The longer the time since unprotected intercourse, the lower the typical effectiveness of hormonal EC methods.
Method Chosen: Different methods have varying efficacy windows and overall effectiveness percentages.
Important Disclaimer: This calculator provides an *estimated* effectiveness and should not replace professional medical advice. Pregnancy is complex, and individual biological factors can influence outcomes. If you have concerns about potential pregnancy, consult a healthcare provider. The Copper IUD has a distinct calculation as its effectiveness remains consistently high for up to 5 days post-intercourse and is a more definitive preventative measure.
When to Use Emergency Contraception
Unprotected sexual intercourse occurred.
Condom broke or slipped off.
Missed birth control pills or other regular contraceptive method.
Forced or coerced unprotected sex.
EC is a critical tool for reproductive health, offering a reliable option to prevent unintended pregnancies.
function calculateEffectiveness() {
var timeSinceIntercourse = parseFloat(document.getElementById("timeSinceIntercourse").value);
var ecMethod = document.getElementById("ecMethod").value;
var resultElement = document.getElementById("result");
var effectiveness = 0;
var message = "";
// Validate inputs
if (isNaN(timeSinceIntercourse) || timeSinceIntercourse < 0) {
resultElement.innerHTML = "Please enter a valid number of hours.";
return;
}
if (ecMethod === "levonorgestrel") {
if (timeSinceIntercourse <= 72) {
// General effectiveness range for LNG within 72 hours
// We'll represent this as a range or an average for simplicity
if (timeSinceIntercourse <= 24) {
effectiveness = 89; // Higher end for first 24 hours
} else if (timeSinceIntercourse <= 48) {
effectiveness = 80; // Mid-range
} else {
effectiveness = 75; // Lower end of range
}
message = "Estimated effectiveness: " + effectiveness + "% to " + (effectiveness + 10) + "% (prevents pregnancies)";
} else {
// Effectiveness decreases significantly after 72 hours
effectiveness = Math.max(20, 75 – (timeSinceIntercourse – 72) * 0.5); // Linear decrease beyond 72 hours, capped at a minimum
message = "Estimated effectiveness: ~" + Math.round(effectiveness) + "% (lower after 72 hours)";
}
} else if (ecMethod === "ulipristal_acetate") {
if (timeSinceIntercourse <= 120) {
// UPA effectiveness is generally higher and sustained longer
if (timeSinceIntercourse <= 72) {
effectiveness = 90; // High effectiveness in the first 3 days
} else if (timeSinceIntercourse <= 96) {
effectiveness = 85; // Still high
} else {
effectiveness = 80; // Effectiveness starts to decrease but still significant
}
message = "Estimated effectiveness: ~" + effectiveness + "% (prevents pregnancies)";
} else {
message = "Ulipristal acetate is generally not recommended or effective beyond 120 hours.";
effectiveness = 0; // Indicate no significant effectiveness
}
} else if (ecMethod === "copper_iud") {
if (timeSinceIntercourse 0) {
resultElement.innerHTML = message;
} else if (ecMethod !== "copper_iud" && timeSinceIntercourse > 120) {
resultElement.innerHTML = "It is highly recommended to consult a healthcare professional. Effectiveness of hormonal methods is very low at this point.";
} else if (ecMethod === "copper_iud" && timeSinceIntercourse > 120) {
resultElement.innerHTML = "Copper IUD insertion is typically not an emergency option after 120 hours.";
}
else {
resultElement.innerHTML = message; // Handles cases with no input or other errors
}
}