To be fruitful and multiply, Ovulation occurs around the middle of a woman's cycle (specifically, in the middle third) You or your wife can keep a record and count the days from the very first day of menstruation
to the day before your wife get next period. Now this is yours wife cycle. This cycle is mostly fixed except in some women, who do not have the perfect cycle.
The next thing is you or your wife have to count 18 days from the last day of your period and note it down. Now is the beginning period of ovulation and the best fertile time to get pregnant. Count 14 days backwards from the completion of the cycle, which is the 16th day for a cycle of 30 days. If your wife have a menstrual cycle of 30 days, your best time in cycle to conceive is from day 12 to 16.
Respected Sir during periods (menstruation) women cannot get pregnant and extremely slims chances to get pregnant.
take care have a great day.