Q. In general what is the phase of the menstrual cycle when copulation may lead to fecundation?

Although this is not a rule, to be effective fecundation in general must occur within about 24 hours after ovulation that occurs around the 14th day of the menstrual cycle. Fecundation may occur even if copulation took place up to 3 days before ovulation since the male gametes remain viable for about 72 hours within the female reproductive system and the fertile period of the women however is considered the period from 7 days before ovulation to 7 days after ovulation.