Continuous oral contraceptives may be more effective than the standard 28-day birth control pills in suppressing the ovary, according to researchers.
They say that the continuous pill also causes a significant improvement in pain and behavioral changes.
"We have provided a biological proof of concept that both the ovary and the lining of the uterus are suppressed better and quicker with the continuous pill than with the cyclic pill. And there is no harmful effect on the lining of the uterus either," said Richard Legro, M.D., professor of obstetrics and gynecology, Penn State College of Medicine and lead author of the study.
Standard 28-day birth control pills mimic a woman's natural menstrual cycle, while preventing pregnancy. A standard dose includes 21 hormone pills to suppress growth in the endometrium, the lining of the uterus, and seven placeholder placebo pills.
Continuous oral contraceptives may be more effective in treating several medical conditions, where continuous ovarian suppression is desired, such as acne, hirsutism, premenstrual syndrome, endometriosis and polycystic ovary syndrome. But there have been few detailed studies of ovarian function on the pill to demonstrate this effect.
Legro and his colleagues compared the effectiveness of continuous oral contraceptives with that of the cyclical pills. The researchers monitored 62 healthy women, randomly assigned to receive either cyclical or continuous birth control pills, for six months with both researchers and participants blinded to the study group.
"We monitored vaginal bleeding, quality of life, and ovarian and endometrial suppression," said Legro, whose team's findings appeared in a recent issue of the Journal of Clinical Endocrinology and Metabolism.
The researchers found a significant decrease in moderate to heavy bleeding days among women who received the continuous birth control regimen. Women in the continuous group also had a significant decline in circulating and urinary estrogen levels, total ovarian volume and lead follicle size – all biomarkers that indicate the ovary is less active – and reported less pain and behavioral changes compared to women in the cyclic group.
However, results from the study also indicate greater breakthrough bleeding, or spotting, among women in the continuous group. Legro says that while greater breakthrough bleeding may be a truly objectionable side effect for many women, it does not seem to affect their quality of life.
"That is one of the unique things of this study. The quality of life did not necessarily decrease as it was counterbalanced by improvements in other areas such as pain and mood swings," the Penn State researcher added.
According to Legro, the study suggests that there may be diverse mechanisms of breakthrough bleeding depending on whether a woman is using either a cyclical or continuous regimen of birth control pills.
In the case of cyclic pills, the ovary comes back into the equation during the pill free interval leading to a rebound increased secretion of ovarian hormones, which in turn contributes to some breakthrough bleeding, he explained.
"Breakthrough bleeding in the continuous group, in our opinion, is most likely due to the fact that the pill does too good of a job in suppressing the ovary and the lining of the uterus gets a little bit thin and fragile so that from time to time there is a little bit of bleeding," added Legro, whose work is funded by the National Institutes of Health.
The study provides a physical reason for continuous oral contraceptive pills to treat such chronic medical conditions such as polycystic ovary syndrome, endometriosis and premenstrual syndrome, where additional suppression of the ovary or the endometrium is desired, and Legro noted that other chronic conditions such as hypertension or diabetes are treated continuously, not three weeks out of four. Further studies showing a favorable risk benefit ratio of continuous oral contraceptives on these disorders are the next step.