Chances of Getting Pregnant After Sex/Data: Difference between revisions

Revision as of 17:25, 16 September 2025

This subpage contains the data and risk models used on the main page. The data is based on population averages and is used to generate a risk estimate.

Baseline Fertility Parameters

These are single-value constants used in the risk model calculation.

Peak Conception Probability (A): 0.33
Fertile Window Width (σ, in days): 2.5
Approximation of 'e': 2.71828

Age-Related Fertility

This table provides a final multiplier based on the woman's age, which adjusts the overall result from the bell curve calculation.

age_description	age_multiplier
Under 25	1.0
25-30	0.9
31-39	0.65
40 and over	0.25

Reference: Age and Fertility: A Guide for Patients, American Society for Reproductive Medicine (ASRM), 2021.

Menstrual Cycle Profile

This table provides the estimated peak ovulation day (μ) for different cycle profiles. A value of -1 indicates an irregular cycle where a peak cannot be reliably predicted.

cycle_description	cycle_ovulation_day_mu
Regular and short (25 days or less)	11
Regular and average (26-31 days)	14
Regular and long (32 days or more)	18
Irregular or I don't know	-1

Reference: Your Menstrual Cycle, Office on Women's Health, U.S. Department of Health & Human Services, 2021.

Timing of Intercourse

This table converts the user's time window into a single day of the cycle (x) for use in the calculation (using the midpoint of the range).

timing_description	timing_intercourse_day_x
1-7 days ago (During or just after my period)	4
8-13 days ago (About a week after my period)	11
14-20 days ago (About two weeks after my period)	17
21-28 days ago (In the week my next period was due)	25
More than 28 days ago	-1

Reference: Based on standard menstrual cycle phases.

Risk Models

This model uses a Gaussian (bell curve) function to estimate risk, approximating the mathematical constant 'e' with 2.71828.

  RiskModel: Chances of Getting Pregnant After Sex/Data:PregnancyRiskPerEvent
    Content: 
{{#ifexpr: {cycle_ovulation_day_mu} < 0 or {timing_intercourse_day_x} < 0
| ''Because your cycle is irregular or the timing is too uncertain, it's not possible to provide a reliable estimate with this tool.''
| Your estimated chance of pregnancy is about '''{{One_In_X|{result}}}''' from this event.
}}

Calculation Explanation: 🔢 This model calculates the distance in days between intercourse (`x`) and the estimated day of ovulation (`μ`), then inputs that distance into a bell curve formula to find the corresponding probability. This result is then adjusted by the age_multiplier. This method more accurately reflects the rise and fall of fertility throughout the cycle.

Initially created by Gemini (Sept. 2025).

@@ Line 1: / Line 1: @@
 This subpage contains the data and risk models used on the [[Chances_of_Getting_Pregnant_After_Sex|main page]]. The data is based on population averages and is used to generate a risk estimate.
-=== Age-Related Fertility ===
+== Baseline Fertility Parameters ==
-This table provides a relative fertility multiplier based on the woman's age. A value of 1.0 represents peak fertility, with lower values representing the average decline in fecundability (the per-cycle probability of conception) with age.
+These are single-value constants used in the risk model calculation.
+* Peak Conception Probability (A): 0.33
+* Fertile Window Width (σ, in days): 2.5
+* Approximation of 'e': 2.71828
+----
+== Age-Related Fertility ==
+This table provides a final multiplier based on the woman's age, which adjusts the overall result from the bell curve calculation.
 <riskdata table="age_data" columns="age_description|age_multiplier">
@@ Line 11: / Line 18: @@
 </riskdata>
-The risk is based on per-cycle conception rates.
+* Reference: [https://www.asrm.org/globalassets/asrm/asrm-content/resources/patient-resources/protect-your-fertility/age-and-fertility.pdf Age and Fertility: A Guide for Patients], American Society for Reproductive Medicine (ASRM), 2021.
-* [https://www.asrm.org/globalassets/asrm/asrm-content/resources/patient-resources/protect-your-fertility/age-and-fertility.pdf Age and Fertility: A Guide for Patients], American Society for Reproductive Medicine (ASRM), 2021.
-* [https://www.acog.org/womens-health/faqs/having-a-baby-after-age-35-how-aging-affects-fertility-and-pregnancy Having a Baby After Age 35: How Aging Affects Fertility and Pregnancy], American College of Obstetricians and Gynecologists (ACOG), 2021.
-=== Timing of Intercourse ===
+----
-This table provides the baseline, single-event probability of conception based on when intercourse occurred relative to the start of the last menstrual period. This model assumes a regular, average-length (28-day) cycle for this baseline data. A value of -1 indicates that the time window is too uncertain to calculate a meaningful probability.
+== Menstrual Cycle Profile ==
+This table provides the estimated '''peak ovulation day (μ)''' for different cycle profiles. A value of -1 indicates an irregular cycle where a peak cannot be reliably predicted.
-<riskdata table="timing_data" columns="timing_description|timing_base_probability">
+<riskdata table="cycle_data" columns="cycle_description|cycle_ovulation_day_mu">
--7 days ago (During or just after my period)|0.01
+Regular and short (25 days or less)|11
--13 days ago (About a week after my period)|0.15
+Regular and average (26-31 days)|14
--20 days ago (About two weeks after my period)|0.33
+Regular and long (32 days or more)|18
--28 days ago (In the week my next period was due)|0.005
+Irregular or I don't know|-1
-More than 28 days ago|-1
 </riskdata>
-The probabilities represent the chance of conception from a single act of intercourse.
+* Reference: [https://www.womenshealth.gov/menstrual-cycle/your-menstrual-cycle Your Menstrual Cycle], Office on Women's Health, U.S. Department of Health & Human Services, 2021.
-* [https://www.nejm.org/doi/full/10.1056/nejm199512073332301 Timing of Sexual Intercourse in Relation to Ovulation — Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby], Wilcox A.J. et al, New England Journal of Medicine, 1995.
-=== Menstrual Cycle Profile ===
+----
-This table provides a multiplier to adjust the risk based on cycle regularity. An irregular cycle makes it difficult to predict ovulation, so the probability is adjusted downward from the "peak timing" assumption to a general average, and the uncertainty is increased. A `cycle_uncertainty_factor` greater than 1.0 triggers a special message.
+== Timing of Intercourse ==
+This table converts the user's time window into a single '''day of the cycle (x)''' for use in the calculation (using the midpoint of the range).
-<riskdata table="cycle_data" columns="cycle_description|cycle_multiplier|cycle_uncertainty_factor">
+<riskdata table="timing_data" columns="timing_description|timing_intercourse_day_x">
-Regular and short (25 days or less)|1.0|1.0
+-7 days ago (During or just after my period)|4
-Regular and average (26-31 days)|1.0|1.0
+-13 days ago (About a week after my period)|11
-Regular and long (32 days or more)|1.0|1.0
+-20 days ago (About two weeks after my period)|17
-Irregular or I don't know|0.2|2.0
+-28 days ago (In the week my next period was due)|25
+More than 28 days ago|-1
 </riskdata>
-The multiplier adjusts the single-event probability.
+* Reference: Based on standard menstrual cycle phases.
-* [https://www.womenshealth.gov/menstrual-cycle/your-menstrual-cycle Your Menstrual Cycle], Office on Women's Health, U.S. Department of Health & Human Services, 2021.
-=== Risk Models ===
+----
-This section defines the calculations and output text for the risk estimates on the main page.
+== Risk Models ==
+This model uses a Gaussian (bell curve) function to estimate risk, approximating the mathematical constant 'e' with 2.71828.
-<riskmodel name="PregnancyRiskPerEvent" calculation="timing_base_probability * age_multiplier * cycle_multiplier">
+<riskmodel name="PregnancyRiskPerEvent" calculation="0.33 * (2.71828 ^ (-0.5 * ((timing_intercourse_day_x - cycle_ovulation_day_mu) / 2.5) ^ 2)) * age_multiplier">
-{{#ifexpr: {result} < 0
+{{#ifexpr: {cycle_ovulation_day_mu} < 0 or {timing_intercourse_day_x} < 0
-| ''Because your last period started more than 28 days ago, it is not possible to provide a reliable estimate. You could be in a low-risk or high-risk phase of your cycle, or you may already be pregnant. Consider taking a pregnancy test if your period is late.''
+| ''Because your cycle is irregular or the timing is too uncertain, it's not possible to provide a reliable estimate with this tool.''
-| {{#ifexpr: {cycle_uncertainty_factor} > 1.5
+| Your estimated chance of pregnancy is about '''{{One_In_X|{result}}}''' from this event.
-  | ''Because your cycle is irregular, your chances are highly variable and difficult to predict. The risk can range from almost zero on non-fertile days to a peak of about a {{One_In_X|{{#expr:0.33 * {age_multiplier} }} }} chance on your most fertile day.''
-  | Your estimated chance of pregnancy is about '''{{One_In_X|{result}}}''' from this event.
-  }}
 }}
 </riskmodel>
-''Calculation Explanation:'' The model calculates the final risk by taking the '''timing_base_probability''' and adjusting it using the multipliers for '''age_multiplier''' and '''cycle_multiplier'''. The model then displays one of three messages based on the result: a specific chance for a standard calculation, a message about variability for irregular cycles, or a message about uncertainty if the timing is unknown.
+''Calculation Explanation:'' 🔢 This model calculates the distance in days between intercourse (`x`) and the estimated day of ovulation (`μ`), then inputs that distance into a bell curve formula to find the corresponding probability. This result is then adjusted by the '''age_multiplier'''. This method more accurately reflects the rise and fall of fertility throughout the cycle.
 ----
+Initially created by Gemini (Sept. 2025).
-Initially created by [[https://gemini.google.com|'''Gemini (Sept. 2025)''']]