Ovulation and Follicular Development Associated With Mid Follicular Phase Initiation of Combined Hormonal Contraception Containing Estradiol Hemihydrate Compared to Ethinyl Estradiol

This study is a randomized control, non-inferiority trial which compare the proportion of ovulation between two oral combined pills when delay starting the first tablet at mid-follicular phase of menstrual cycle in 18 - 40 year old, healthy women with prior normal and regular periods. Participations will be undergone trans-vaginal or trans-rectal ultrasonography between day 1 - 3 of menstrual period for evaluation of ovarian follicle/cyst (if present). Only women who have normal looking of ovaries without dominant ovarian follicle will be included in study-protocol. Immediately after trans-vaginal/trans-rectal ultrasound between day 7 - 9 of menstrual period, all participants will be randomly assigned to receive one pack of investigated pills (1.5 mg estradiol hemihydrate/2.5 mg nomegestrol acetate or 20 mcg ethinyl estradiol/75 mcg gestodene) and to take the first tablet under direct observation by research-nurse. Participants will take one consecutive tablet at about the same time each day until complete pack. The next appointments will be every 2 - 3 days to monitor ovarian function by using Hoogland score until ovulation or follicular quiescence will be presented. The last visit will be about 1 week after complete pack to monitor adverse effect and safety through out the protocol.