If i had unprotected sex during ovulation, how effective will emergency contraceptive taken within 52 hours be to prevent pregnancy?

Yes: Plan B can work in one of three ways depending on where you are in your cycle. It can prevent or delay ovulation, can interfere with the fertilization of the egg or may prevent implantation by altering the lining of the uterus. If you take Plan B One-Step within 24 hours, it is about 95% effective.

"Up to 89%": Information about the effectiveness of the Morning-After Pill or Plan B One-Step is that the progestin/levonogestrel pills are up to 89% effective when taken within 72 hours of unprotected sex. Some effectiveness remains up to 120 hours after. Investigate more reliable methods of contraception; Morning-after pill should rarely be taken. Good wishes!

Fairly effective: The morning-after-pill usually reduces the chance of pregnancy approximately 50% from baseline, and the chances of pregnancy from unprotected sex at the time of ovulation would be 10-30%. So, with the emergency contraception, in theory, the chance of getting pregnant would be 5-15%. However, people exist in reality, not theory, so your chance could vary. Best to use effective birth control always.

About 90%: However studies have shown "Plan B" is less effective in women over 165#, and in women above that weight. See your OB-GYN if you have concerns, and always use a condom if you are sexually active!

Better than nothing: The concept by Plan B and other products is to prevent implantation of a possible fertilized ovum by making the endometrium inhospitable. The delay of 52 hours may or may not succeed, but is proactive and better than nothing.