Natural conception calculator - Dr Dimitrios Mavrelos

Natural (spontaneous) conception calculator

Estimates the chance of a spontaneous ongoing pregnancy leading to live birth within 12 months for a subfertile couple, using the revised natural-conception prediction model (Bensdorp et al. 2017), an update of the validated Hunault “synthesis” model behind freya.nl.

Inputs

Female age (years) Duration of subfertility (years) Cycle length (days) Basal FSH (IU/l) Female BMI (kg/m²) Tubal status Referral Pregnancy history (current relationship)

Each previous pregnancy is a favourable sign — tick all that apply.

Previous ongoing pregnancy Previous miscarriage Previous termination Previous pregnancy via fertility treatment Male partner: pregnancy in a previous relationship

Semen analysis (optional — defaults to normal)

Semen volume (ml) Progressive motility (%) Concentration (normalised, 40 = normal)

Follows the published score chart's scaling (not million/ml).

Normal forms / morphology (%)

Result

1-year chance of natural ongoing pregnancy

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Total score

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Prognosis category

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Predictor	Value	Points

The 30% threshold is the guideline cut-off below which fertility treatment (e.g. IUI with stimulation) may be considered; above it, expectant management for 6 months is often as effective.

References

#	Source	Note
1	Bensdorp AJ et al. A revised prediction model for natural conception. RBMO 2017;34:619–626	Source of the score chart implemented here (5,184 couples; c-statistic 0.71). Female age up to 45.
2	Hunault CC et al. Two new prediction rules for spontaneous pregnancy. Hum Reprod 2004;19:2019–2026	The original validated synthesis model this revises.
3	freya.nl natural-conception calculator	Patient-facing implementation of the Hunault model.

Disclaimer

This is an educational estimate for subfertile couples based on a published prediction model, not a personalised diagnosis or guarantee. It reproduces the exact Bensdorp 2017 score chart, which predicts unassisted (natural) conception within 12 months in a subfertile population who have completed a fertility work-up (overall ~20–26% in the source cohort), so figures are deliberately lower than general-population fertility. Tubal-testing status is a major factor (untested tubes score higher than tested-normal). The model was developed in couples with ovulatory cycles, no double-sided tubal blockage, and female age under 45, and has not been re-validated in every population. It does not replace clinical assessment. Please discuss your individual situation with your fertility specialist.