Effectiveness of levonorgestrel emergency contraception given before or after ovulation--a pilot study

Area of Science:

• Reproductive endocrinology
• Pharmacology of emergency contraception

Background:

• The precise mechanisms of action for levonorgestrel emergency contraceptive pills (LNG ECP) remain incompletely understood.
• Existing research suggests LNG ECP primarily functions by inhibiting ovulation.

Purpose of the Study:

• To investigate the efficacy of LNG ECP based on its timing relative to ovulation.
• To determine if LNG ECP affects fertilization or implantation.

Main Methods:

• Ninety-nine women seeking emergency contraception received a single 1.5 mg dose of LNG.
• Serum hormone levels (LH, estradiol, progesterone) were measured to accurately determine ovulation timing.
• Participants were followed up to assess pregnancy status, comparing outcomes based on intercourse and ECP timing relative to ovulation.

Main Results:

• A pregnancy rate of 3.0% was observed.
• All pregnancies occurred when LNG ECP was taken two days after ovulation.
• No pregnancies were observed when LNG ECP was taken before or on the day of ovulation, despite intercourse during the fertile window.

Conclusions:

• Levonorgestrel emergency contraceptive pills are most effective when administered prior to ovulation.
• LNG ECP demonstrates minimal to no impact on post-ovulatory events such as fertilization or implantation.