May 11, 2012 -- Women who use non-oral hormonal contraceptives, like patches and vaginal rings, may be at higher risk of blood clots than those who take oral forms of birth control, according to a new Danish study published in the journal BMJ.
Researchers from the University of Copenhagen analyzed national data from more than 1.6 million healthy women ages 15 to 49 who took various forms of birth control. They found that women who took birth control pills were at three times the risk of blood clots than those who did not use any type of hormonal birth control, but those who used other types of non-oral hormonal contraceptives were at higher risk. Women who used skin patches were at eight times an increased risk of blood clots and those who used vaginal rings had a 6.5 percent increased risk.
Patches and vaginal rings continuously releases hormones into the body to prevent pregnancy. The study suggests that some women talk with their doctor about switching from non-oral hormone contraceptives if they are already at high risk for blood clots.
People who are overweight, inactive, those who smoke and have a family history of blood clots are all at increased risk. Certain medical conditions also increase a person's risk.
"The important thing is that women are informed about the risk of VT for different product types," said Øjvind Lidegaard of the University of Copenhagen and lead author of the study. "Then I think they can decide themselves whether they want to continue of switch to another product. For young women, the most obvious alternative is a low-dose second-generation pill with levonorgestrel."
Almost half of all pregnancies in the U.S. are unintended, according to the Centers for Disease Control and Prevention. About 10.7 million women in the U.S. use birth control pills.
But experts noted the limitations of the study, pointing out that the research did not account for excess fat and smoking habits, both recognized risk factors of blood clots.
Dr. Paula Hillard, professor of obstetrics and gynecology at Stanford University School of Medicine, noted that the risk of venous thrombosis during pregnancy can be much higher than the numbers tallied in the study.
"The combined hormonal contraceptives, even those that the authors found to have an increased risk of venous thrombosis compared to other specific combination oral contraceptives, are associated with a higher risk than an individual would experience if she were pregnant," said Hillard. "Thus, preventing unintended pregnancy is health promoting."
While non-oral hormonal contraceptives did indeed show a higher risk of blood clots, Hillard said individuals must consider which option is best and most effective.
"The patch and the ring are methods that may be more effective at preventing pregnancy compared to methods that require daily use of a pill, which is difficult to take correctly and consistently day in- and day out," said Hillard.
Of note, authors found that intrauterine devices, or IUDs, a T-shaped plastic or copper device that is placed in a woman's uterus to prevent pregnancy, was not associated with blood clots. In fact, researchers said they were associated with a reduced risk and may have a protective effect against blood clots.
"Thus when discussing contraceptive options with women who might consider switching, the option of an IUD offers not only a method that is as effective as sterilization at preventing unintended pregnancy, and which lasts five or 10 years, but that also has a lower risk of venous thrombosis," said Hillard.