Probability of Conception in the First Menstrual Cycle
For a healthy couple under 35 years old with regular cycles and normal semen parameters using timed intercourse, the probability of conception in the first cycle is approximately 20-25%, with cumulative pregnancy rates reaching 61% by 6 cycles and 74-79% by 12 cycles. 1, 2
Per-Cycle Conception Probability
- The per-cycle probability of pregnancy (fecundability) for healthy couples attempting conception is approximately 20-25% per menstrual cycle when intercourse is properly timed to the fertile window 1, 3
- This assumes the couple has no fertility problems and the woman is under 35 years of age with regular ovulatory cycles 2, 4
- The probability that a single act of intercourse occurs within the fertile window is approximately 25%, with the fertile window spanning 6 days ending on the day of ovulation 3, 5
Cumulative Pregnancy Rates Over Time
By 6 cycles of attempting conception:
- Women under 35 years achieve a cumulative pregnancy probability of 61-62% 1, 2
- For optimal conditions (age <35, regular cycles with <5 days variation, frequent intercourse), this increases to 88% 1
By 12 cycles of attempting conception:
- Women aged 21-27 years achieve cumulative pregnancy rates of 74-79% 1, 2
- For optimal conditions, this increases to 95% 1
- The median time to pregnancy is approximately 4 cycles for the general population under 35 1
Factors That Maximize First-Cycle Success
Optimal intercourse timing:
- Couples should have intercourse every 1-2 days beginning soon after menstrual bleeding stops to maximize coverage of the fertile window 5, 6
- The most fertile days are cycle days 8-19 in a standard 28-day cycle 5
- Conception is most likely when intercourse occurs during the 6-day window ending on the day of ovulation, characterized by slippery, stretchy cervical mucus 5, 7
Age considerations:
- Female age under 35 years is associated with the highest fecundability, with a nearly monotonic decline after age 33 2
- Women aged 21-24 years have the highest per-cycle conception rates, with fecundability ratios declining to 0.87 by ages 31-33 and 0.60 by ages 37-39 2
Important Clinical Caveats
Cycle viability variation:
- Not all menstrual cycles are viable for conception—on average, less than half of cycles result in a fertilizable ovum even with optimal timing 7
- This biological reality means that even with perfect timing, conception may not occur in the first cycle
Sperm and ovum survival:
- Sperm can survive up to 5 days in the female reproductive tract, with an average survival time of 1.4 days 7
- The ovum remains viable for approximately 0.7 days after ovulation 7
- This creates a practical fertile window where intercourse 5 days before ovulation through the day of ovulation can result in conception 7
When to seek evaluation:
- Infertility evaluation is recommended after 12 months of regular unprotected intercourse for women under 35 years 6, 5
- For women 35 years or older, evaluation should begin after 6 months of attempting conception 6, 5
Lifestyle factors to avoid: