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Chances of Getting Pregnant After Sex/Data

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Revision as of 23:24, 15 September 2025 by Gavinandresen (talk | contribs) (Better version of the page from Gemini)

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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