This was a prospective, open-label, single-drug, uncontrolled, observational clinical study.

Women attending the Family Planning Association of Hong Kong (FPAHK) for emergency contraception within 120 hours of UPSI were recruited. Subjects were recruited from both the Birth Control Clinics and Youth Health Care Centres of the FPAHK.

Depending on the timing in relation to ovulation in the current menstrual cycle at the time of presentation, the women were classified into two groups:

Group 1: pre-ovulatory Group 2: post-ovulatory

After counseling and obtaining informed consent, eligible subjects received a single dose of ulipristal acetate 30 mg (ellaOne®) under direct supervision. A baseline blood test for hormonal profile (LH, oestradiol and progesterone) and ultrasound scan for ovarian follicle assessment were carried out by a designated doctor or research nurse at the clinic visit.

The subjects were advised not to have further acts of coitus before the return of menstruation. They were given a diary chart to record vaginal spotting and bleeding, possible side effects and further acts of intercourse, if any, and the contraceptive method used. A follow-up appointment were be arranged about 1-2 weeks after the expected next menstruation. Any events of unplanned pregnancy and adverse effects were recorded for analysis.

Inclusion Criteria:

1. Healthy women aged 18 years or above;
2. Regular menstrual cycles (every 21-35 days) within the past three cycles;
3. Requesting emergency contraception within 120 h of a single act of unprotected intercourse in the current menstrual cycle;
4. Willing to abstain from further acts of unprotected intercourse and;
5. Available for follow-up over the next 6 weeks

Exclusion Criteria:

1. Post-abortion or postpartum patients whose period had not yet returned
2. Regular use of prescription drugs before admission to the study and
3. Intercourse during the treatment cycle more than 120 h before admission into the study.
4. Found pregnant at the time of presentation
5. Breastfeeding women
6. Women who have been sterilized (or partner being sterilized) or have intrauterine contraceptive device in-situ
7. Uncertain about the date of the last menstrual period
8. Women who had used hormonal contraceptive in the current or past one cycle

A total of 700 women attending the Family Planning Association of Hong Kong for emergency contraception who fulfilled the inclusion criteria and not meeting the exclusion criteria were recruited.