The optimal conception time windows are different for sperm and oocyte. The optimal time for fertilizing an oocyte is between 37-42 hours after the trigger (or start of an LH surge) or in other words, from the moment of ovulation + 5 hrs. It takes a sperm cell about 10 minutes after ejaculation to reach the oocyte and another 30 minutes for capacitation. Human sperm cells may retain the ability to fertilize an oocyte for two to three days after ejaculation.
Best time of conception for oocyte
The human oocyte has a fertilization window of about 20 hours counting from ovulation. The chance of fertilization increases up to at least 12 hours after ovulation, but the chance that the fertilization will lead to a viable pregnancy is the highest in the first 5 hours and then begin to slowly decrease.
The time of expected ovulation must be counted from the beginning of the LH rise. Once LH begins to rise, it may remain elevated for more than 24 hrs. Often, the entire duration of LH elevation is incorrectly referred to as a peak. In reality, since LH is usually measured once a day, it is impossible to say that it was measured at the peak or at the margins. For practical purposes, once LH is first detected to be rising, ovulation time can be estimated according to the drawing below.
Best time of conception for sperm
After ejaculation, it takes a sperm only a few minutes to reach a meeting place with the oocyte. Human sperm retains the ability to fertilize an oocyte for 1-3 days after ejaculation inside of the woman’s body. Interestingly, in vitro, at room temperature, some sperm cells may remain motile for 3 weeks!
Optimal overlap between best time for sperm and oocyte
The chance of viable conception can be increased by two intercourses timed by about a day apart. The second ejaculate after short abstinence will usually have fewer sperm cells, but they will be of better quality. A good strategy would be to abstain long enough to be able to ejaculate two times in a row, one day apart or less.