A woman can become pregnant when a sperm fertilizes an egg, which usually occurs during a woman’s fertile window. This window includes the day of ovulation and the days leading up to it. Ovulation usually occurs about halfway through a woman’s menstrual cycle, about 12 to 16 days before her next period begins.
So, if you are asking which “cycle” or phase of the cycle can lead to pregnancy, it would be around ovulation. However, sperm can stay inside the female reproductive tract for up to five days, so intercourse in the days leading up to ovulation can also result in pregnancy. If you have more specific questions about fertility or conception, feel free to ask!