Standard birth control pills contain two hormones: progestogen and estrogen. One-phase birth control pills contain the same dose of progestogen and estrogen every day. Four-phase birth control pills contain different amounts of progestogen and estrogen on different days. This review looked at how well one-phase birth control pills and four-phase birth control pills work to prevent pregnancy, how often they cause bleeding problems, how often users experience side effects and how many women stop using the pills.
We did a computer search for randomized controlled trials comparing four-phase birth control pills with one-phase birth control pills. We also wrote to researchers and makers of birth control pills to find other trials. Studies had to report on pregnancy, bleeding problems, side effects or stopping the use of pills. We did not include studies where the pills were used as a treatment for disorders like acne, hirsutism, polycystic ovary syndrome, bleeding problems or endometrioses, or where the pills were administered for less than three months. We assessed whether the studies were conducted properly.
We included one study comparing a four-phase pill composed of the progestogen dienogest and the estrogen estradiol valerate with an one-phase pill composed of the progestogen levonorgestrel and the estrogen ethinylestradiol. Four-phase birth control pills and one-phase birth control pills had similar pregnancy rates. The number of women with blood loss in the period between two menstruations was similar for four-phase pills and one-phase pills. More women using one-phase birth control pills had a menstruation compared to women using four-phase birth control pills. The number of women who stopped using the pills because of side effects was similar for four-phase pills and one-phase pills. Breast pain was reported more frequently by women who used four-phase birth control pills than women who used one-phase birth control pills.
The presence of only one study made it impossible to adequately compare four-phase birth control pills with one-phase birth control pills. More studies are needed to determine whether four-phase pills have advantages over one-phase pills. Until then, we recommend one-phase pills containing 30 μg estrogen for women starting to use birth control pills.