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

Objective To determine effects of continuous vs cyclic oral contraception.

Design Randomized double blind trial

Setting Academic medical center in Pennsylvania

Patients 62 healthy women with regular menses

Intervention Cyclic oral contraception (21d active/7d placebo given for 6 consecutive 28d cycles) versus continuous (168d of active pill) therapy using a monophasic pill (20 mcg ethinyl estradiol and 1 mg norethindrone actetate).

Main Outcome Measures Primary outcome was vaginal bleeding, 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 cyclic regimen (mean 11.0d [SD 8.5d], versus continuous 5.2d [6.8d]; P = 0.005), with both groups decreasing over time. Endogenous serum and urinary estrogens measured over 6 cycles was significantly lower (P = 0.02) in the continuous group than the cyclic 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 exams. 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 168d period of observation, but provides greater suppression of the ovary and endometrium. These effects are associated with improved patient symptomatology.