Intercourse first time

The primary difficulty with periodic abstinence is the month-to-month variation in the time of ovulation. Whereas the ovum can only be fertilized during the first 12 to 24 hours after its release from the ovary, sperm remain viable longer in the female reproductive tract, able to fertilize an ovum for 5—7 days and perhaps longer. Thus, intercourse several days prior to ovulation can result in pregnancy. 

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