FSH and ovarian response: spontaneous recovery of pituitary-ovarian activity during the pill-free period vs. exogenous recombinant FSH during high-dose combined oral contraceptives.

OBJECTIVE: Compare spontaneous recovery of pituitary-ovarian activity during the pill-free period following the correct use of low-dose oral contraceptives and subsequent ovarian function during the administration of exogenous recombinant FSH (recFSH) after switching to continued Lyndiol (2.5 mg lynestrenol + 0.05 mg ethinyl-oestradiol) medication.

DESIGN: Prospective, randomized, group-comparative, single-centre study. Following the monitoring of the pill-free period (week 1) and subsequent treatment with Lyndiol (for a total of 5 weeks), all subjects were randomly allocated to one of four groups receiving daily FSH injections for 1 week [75, 150, 225 IU recFSH or 150 IU purified urinary FSH (uFSH)] during the fourth week of Lyndiol use.

PATIENTS: Thirty-six healthy volunteers aged 18-39 years, prestudy oral contraceptive use for at least 3 months, cycle length between 24 and 35 days.

MEASUREMENTS: Serum FSH, LH and oestradiol (E2) concentrations as well as transvaginal ultrasound assessment of the number and diameter of follicles > 2 mm were used to monitor pituitary ovarian function.

RESULTS: At the start of the pill-free period following the prestudy contraceptive medication, 67% of the women presented with LH and FSH levels < 1 IU/l and only one follicle > 10 mm was observed. Initial levels of LH and FSH correlated (P < 0.05) with the extent of pituitary-ovarian activity during the pill-free period. At the end of the pill-free period a follicle > 10 mm had emerged in one subject only. During the first 3 days of Lyndiol use, seven women (19%) eventually showed at least one follicle > 10 mm. During combined exogenous FSH and Lyndiol administration, LH levels remained completely suppressed (< or = 0.5 IU/l) in all women studied. FSH levels and number and size of follicles increased with increasing doses of exogenous FSH in a dose-dependent manner. E2 levels remained low in all groups (< 150 pmol/l). During the week following FSH administration, FSH levels and E2 levels decreased gradually while the number of follicles > 10 mm still increased.

CONCLUSIONS: We have confirmed that dominant follicles > 10 mm are present at the end of the pill-free period and during the first days after resumption of pill intake. Once follicles > 10 mm arose at the end of the pill-free period, continued use of Lyndiol did not reduce follicle diameters. One week of Lyndiol reduces pituitary-ovarian activity to levels observed after 3 weeks of low-dose pills. FSH administration during Lyndiol resulted in dose-dependent follicle growth despite extremely low LH levels. E2 secretion (56 +/- 51 pmol/l) occurred to a limited and variable extent along with extremely low serum LH concentrations. Recovery of pituitary-ovarian activity at the end of the pill-free period is comparable to FSH levels and follicle dynamics following 7 days of 75-150 IU/l recFSH.