Optimal Timing of Intercourse for Conception
For couples trying to conceive, intercourse should occur during the 6-day fertile window ending on the day of ovulation, with the highest probability of conception occurring on the day before ovulation. 1, 2
Understanding the Fertile Window
The fertile window spans approximately 6 days in each menstrual cycle, beginning 5 days before ovulation and ending on the day of ovulation itself. 3, 2 After correcting for measurement error in identifying ovulation, both major studies confirm this same 6-day interval, with conception probability falling to essentially zero after ovulation occurs. 2
Day-specific conception probabilities are highest on the day immediately before ovulation, with significant probabilities also present from 5 days before ovulation through ovulation day. 3, 2 Sperm can survive an average of 1.4 days in the female reproductive tract, with a 5% probability of surviving more than 4.4 days and only 1% probability of surviving beyond 6.8 days. 3
Evidence-Based Timing Strategies
Urinary Ovulation Prediction Kits
Timed intercourse using urinary ovulation tests probably increases live birth rates compared to intercourse without ovulation prediction (RR 1.36,95% CI 1.02 to 1.81), meaning if baseline live birth chance is 16%, using ovulation kits increases this to 16-28%. 1
These kits also probably increase overall pregnancy rates (clinical pregnancy or positive urine test) with a risk ratio of 1.28 (95% CI 1.09 to 1.50), translating baseline pregnancy rates from 18% to 20-28%. 1
Fertility Awareness-Based Methods (FABM)
Evidence is insufficient to determine whether FABM (including basal body temperature tracking, cervical mucus monitoring, or calendar apps) improves live birth rates compared to intercourse without ovulation prediction (RR 0.95% CI 0.76 to 1.20). 1
Methods that prospectively identify the fertile window before it occurs are more effective than retrospective methods like basal body temperature, which only confirms ovulation after it has already happened. 4, 2 Cervical mucus assessment can anticipate ovulation by several days and would be particularly useful for timing intercourse. 2
Practical Recommendations
Frequency of Intercourse
Rather than precisely timing single acts of intercourse, couples should aim for intercourse at least 2-3 times per week throughout the cycle. 5 This approach ensures coverage of the fertile window without the stress and potential missed opportunities associated with attempting to time a single act of intercourse. 5
The recommendation for frequent intercourse (couple of times per week) not only reduces stress but also ensures coitus during the period with greatest conception probability, as much of the peak fertility period is missed when relying solely on calendar calculations, basal body temperature, or even LH kits. 5
Avoiding Common Pitfalls
Do not rely on basal body temperature charts for timing intercourse, as they identify ovulation retrospectively after the fertile window has already passed. 4, 5 Calendar calculations similarly miss much of the peak fertility period. 5
Be aware that timed intercourse recommendations can significantly increase stress for couples, which may actually hinder normal reproductive functioning. 5 The psychological burden is compounded when expensive ovulation prediction methods are used, yet there is limited high-quality evidence demonstrating increased pregnancy rates justify this added stress. 5
Clinical Context
Approximately 89% of couples not using contraception become pregnant within one year, with this estimate adjusted to 85% for those discontinuing reversible contraception. 6 Only about half of menstrual cycles are viable (capable of resulting in pregnancy even with optimal timing), though this varies significantly between women. 3
The evidence supporting urinary ovulation tests comes primarily from women under 40 years old who have been trying to conceive for less than 12 months, so extrapolation to other populations should be done cautiously. 1