Residual ovarian activity during oral contraception

textabstractThe study objectives in this thesis focus on pituitary-ovarian activity in women using oral contraceptive steroids. Contraceptive steroids influence the hypothalamic-pituitary-ovarian axis in order to interfere with normal follicular development and ovulation. Additional effects on the endometrium and cervical mucus may also attribute to the contraceptive effects established by contraceptive steroids. Despite the described additional effects on which the ultimate contraceptive efficacy is based, inhibition of ovulation provides a most reliable form of contraception. The first objective was to review the current knowledge on residual ovarian activity in users of oral contraceptive steroids (see chapter 2). The first study (described in chapter 3) was performed to evaluate to relative importance of dosage of ethinyl-estradiol and type of progestin regarding pituitary-ovarian activity during the pill-free period in users of lowdose combined oral contraceptives. The second study was performed to compare recovery of the pituitary-ovarian activity during the pill-free interval with the ovarian response obtained from different dosages of recombinant FSH during high-dose combined oral contraceptives (chapter 4). The third and fourth study were performed to evaluate the effect of a single dose of an antiprogestin during continuous progestin-only contraception: Both the effects on the pituitaryovarian axis (chapter 5) and the effects on endometrial characteristics and bleeding patterns (chapter 6) are described. Conclusions derived from the studies described in this thesis are presented in the general discussio