In an attempt to increased fertility and chance of conception, equations and medical history are used to evaluate optimal fertility windows for women seeking IVF/ICSI treatment. Even with advanced mathematical and medical tools, the exact date of ovulation and conception are just estimates, as there is no way to pinpoint the exact time and date of conception. Researchers from the Hospital Necker-Enfants Malades and Universite Paris Descartes in Paris recently published a study in the journal Human Reproduction on their findings regarding fertility windows, including day-specific fertility estimations.

Study participants were all treated at the same medical institution for pregnancy screening during the first trimester. In all 5,830 cases were evaluated over a three-year timeframe. All women presented with a particular last menses date.

Conclusion: Researchers were able to identify specific cycle days when the women were most fertile and least fertile. At day two of the cycle, there was a 2% chance of conception. That number rose dramatically by day 12 at 58%. After peaking, fertility dropped to 5% by day 21 and back to 0% by day 25. Early cycle conception occurred in women who were older, experiencing regular cycles, white and black.

Source: Stirnemann JJ, Samson A, Bernard JP, Thalabard JC. Day-specific probabilities of conception in fertile cycles resulting in spontaneous pregnancies. Hum Reprod. 2013 Jan 25.