Pituitary-ovarian activity when switching from various monophasic pills to a triphasic pill

This study was prompted by the various recommendations given by different oral contraceptive manufacturers to women who wish to switch from a monophasic to a triphasic formulation. Ten women who switched from a variety of monophasic pills to a levonorgestrel triphasic pill formulation after a 7-day pill-free interval were studied. Follicular maturation was monitored by ultrasound scan, and the levels of serum follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P) and estradiol (E2) measured. Pituitary-ovarian activity was suppressed in six of the ten women studied, while in the remaining four women there was some pituitary-ovarian activity during the first 10 days on the triphasic pill. These findings suggest a shorter pill-free interval, as advised in USA data sheets, may be less likely to result in pill failures when women switch from a monophasic to a triphasic preparation.