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After release, the egg moves to the fallopian tube, where it stays for 24 hours or more.
Pregnancy occurs if sperm travels to the fallopian tube and fertilizes the egg during this time. If sperm does not fertilize the egg, the egg moves to the uterus and breaks down, ready to leave the body during the next menstrual period.
Females are most fertile within a day or two of ovulation, which is when the ovaries release an egg. But, it is possible to get pregnant in the days leading up to ovulation, as sperm can survive for several days inside the female body.
The days of the menstrual cycle where a woman is least likely to get pregnant is sometimes called the ‘safe period’.
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In this article, we describe how to calculate the fertile window to aid or avoid conception.
Signs of ovulation
Tracking the signs of ovulation can help someone determine the precise day they ovulate each month.
Signs include:
- mild cramping in the lower abdomen
- wetter, clearer, and more slippery vaginal discharge similar to egg white
- a small increase in basal body temperature
- a higher sex drive
Some of these signs, such as basal body temperature, will continue to change after ovulation has occurred. For this reason, a person should not use temperature to predict the fertile window.
It may be helpful for someone to track the signs over a few months to get an idea of what is normal for their body.
But they should keep in mind that there are several variables, and the timing of ovulation can change, month-to-month.
Another option is to use an ovulation predictor kit or fertility monitor.
Fertility aids measure the levels of specific hormones in the urine to determine the ovulation day each month. Some devices also identify days of peak fertility.
Using a combination of these methods may provide an individual with the best accuracy.
Calculating ovulation
Research has shown that ovulation takes place around 14 days before a person expects to have their next period if their monthly cycle is 28 days.
Most people ovulate between days 11 and 21 of their cycle. The first day of their last menstrual period (LMP) is day 1 of the cycle. Ovulation does not always occur on the same day every month and can vary by a day or more on either side of the expected date.
Doctors call the part of the cycle around ovulation the fertile window because a woman’s chance of pregnancy is highest at this time. For example, if a woman ovulates on day 14, they can conceive on that day or within the following 24 hours.
However, their fertile window began a few days before ovulation because sperm can survive for up to 5 days inside the female body. So, even if a woman does not have sex on day 14 or 15, it is still possible to become pregnant if they had unprotected sex on days 9 to 13.
The following table summarizes a typical menstrual cycle and how fertile a person is likely to be at each stage:
Day of cycle Stage Fertility
1–7 Menstruation Least fertile stage
8–9 Post-menstruation Possible to conceive
10–14 Days around ovulation Most fertile
15–16 Post-ovulation Possible to conceive
17–28 Thickening of uterine lining Less fertile — unlikely to conceive