Based on an Internet fertility map, I ovulated on July 15th and my boyfriend and I had intercourse on the 16th. Can I become pregnant the day after ovulation?

Once ovulation occurs, the egg, or ovum, will only be alive for 24 hours and it is most likely to be successfully fertilized in the first 12 hours.

When you calculate your ovulation day based on a fertility map, this is an approximation based on your cycle length, and is not completely accurate. On any given cycle, ovulation can occur a few days earlier or later than expected due to daily fluctuations, diet, stress, travel, etc. 

When one uses the rhythm method this is based on the concept that intercourse after ovulation is much less likely to lead to conception than intercourse prior to ovulation, and it works best with people with very regular cycles. However, the failure rate with the rhythm method is significant.

If you have unprotected intercourse within 2 to 3 days of when you believe you ovulated and you do not wish to be pregnant, it is best advised to take emergency contraception or the "morning after pill" which can be used up to 72 hours after intercourse and still be successful. Your doctor can phone this medication into your local pharmacy if necessary. If you are trying to conceive, good luck!

Answered by Dr. Lynn Friedman, M.D.