Effects of continuous versus cyclical oral contraception: a randomized controlled trial.

Context: Continuous oral contraception may better suppress the ovary and endometrium, lending itself to the treatment of other medical conditions.

Objective: Our objective was to determine the effects of continuous vs. cyclical oral contraception.

Design: This was a randomized double-blind trial.

Setting: This trial was performed at an academic medical center in Pennsylvania.

Patients: A total of 62 healthy women with regular menses were included in the study.

Intervention: Cyclical oral contraception (21-d active/7-d placebo given for six consecutive 28-d cycles) vs. continuous (168-d active pill) therapy using a monophasic pill (20 microg ethinyl estradiol and 1 mg norethindrone acetate) was examined.

Main Outcome Measures: The primary outcome was vaginal bleeding, and secondary outcomes included hormonal, pelvic ultrasound, quality of life, and safety measures.

Results: There was no statistically significant difference in the number of total bleeding days between groups, but moderate/heavy bleeding was significantly greater with the cyclical regimen [mean 11.0 d (sd 8.5) vs. continuous 5.2 d (sd 6.8); P = 0.005], with both groups decreasing over time. Endogenous serum and urinary estrogens measured over six cycles were significantly lower (P = 0.02 and 0.04, respectively) in the continuous group than the cyclical group. Women in the continuous group also had a smaller ovarian volume and lead follicle size over the course of the trial by serial ultrasound examinations. The Moos Menstrual Distress Questionnaire showed that women on continuous therapy had less associated menstrual pain (P = 0.01) and favorable improvements in behavior (P = 0.04) during the premenstrual period.

Conclusions: Continuous oral contraception does not result in a reduction of bleeding days over a 168-d period of observation but provides greater suppression of the ovary and endometrium. These effects are associated with improved patient symptomatology.