In the fall of 2022, stories of blood clots related to birth control use had a moment on TikTok. One such story was of 19-year-old Sydney Marshall, an otherwise perfectly healthy teen who developed a blood clot in her brain. Her doctors attributed the clot to 2 years of hormonal birth control use. The clot was only discovered when Marshall went to the ER for a persistent migraine unrelieved by pain medication, and she was warned that without blood thinner medication the clot would likely eventually have caused her to have a stroke.
Among the 15,000+ comments on Marshall’s viral TikTok video about her experience, many anecdotally corroborated her experience, reading “Same thing happened to me. I had a stroke last year and now have a blood clotting condition caused by my birth control,” and “I am a nurse and have seen many blood clots in the brain and lungs from birth control.” and “Saaaame thing happened to me. it’s alarming how many women are going through this now!” and “I had a pulmonary embolism from mine at age 24! I hate that you’re going through this! Thank you for bringing awareness!”
While we’ve covered the risks of blood clots with hormonal birth control (HBC) use many times before here at Natural Womanhood, a recent literature review determined that higher body mass index (BMI) can significantly increase this risk, highlighting how HBC is not “one size fits all,” and why a person’s overall health and health conditions must be carefully considered when making medical decisions [1]. Given that 39.7% of 20-39 year old women in the U.S. and 43.3% of 40-59 year old women are obese, this topic impacts many women who may be using or considering starting HBC.
What did this literature review look at and what were the results?
The review examined data from multiple other studies that looked at the relative risk of experiencing adverse cardiovascular outcomes (such as blood clots) for women who were overweight or obese, for women using combined oral contraceptives (COCs), and for women who were both obese and using COCs. Researchers combed through numerous large-scale data collection studies such as the national historical registries from Denmark, data from national population and prescribing practices in the United Kingdom, a study that collected data from various Anticoagulation Clinics in the Netherlands, a separate study on blood clots from the Netherlands that included approximately 9,000 subjects, and data from the World Health Organization.
Relative risk for DVT in obese and overweight women
First, the review estimated that the relative risk for developing deep vein thrombosis (DVT, referring to a blood clot that forms in a major vein in the body, usually in the legs) for women of reproductive age (defined here as 40 years or less) was about 6.1x greater for obese than non-obese women of reproductive age. This is significantly higher than the relative risk of developing a blood clot among women who were overweight but not obese, which Severinses et al. found ranged from 1.45–2.82, depending on the specific BMI of the woman [2].
Relative risk for DVT in COC users
Next, the reviewers considered the relative risk of developing DVT for women using combined oral contraceptives (COCs) and found that risk varied depending on the active ingredients and type of contraception, but ranged from a three to seven-fold increase (3x increase for levonorgestrel, which is in Plan B or the morning after pill and Seasonique, Seasonale, Aviane, Lessina, and over 40 other formulations, and a 6–7x increase for: 1) desogestrel, which is in Linessa, Apri, Azurette and 20 other birth control pills, 2) gestodene, which is in Meliane and Gynera, 3) drospirenone, which is in Opil, Yaz, Yasmin, and Zarah, plus 8 other pills, 4) cyproterone, which is in Androcur, Diane, Cleo-35, and Cyestra-35).
Synergistic effect dramatically increases relative risk of DVT in obese or overweight women on COCs
If the mechanisms involved in the increased risk of cardiovascular disease with body mass and contraceptive use are separate, we might expect that the rate for combining these two risk factors would equal each factor added together, so somewhere between 4.5 and 10 times for overweight COC users compared to non-overweight women not using COCs, and somewhere between a 9 and 13 times increase for obese COC users compared to non-obese women not using COCs. What this review actually found was that obesity combined with COC use resulted in a 12 to 24 times increase in the relative risk of developing DVT compared to non-obese, non COC users.
Because this represents a greater risk than each factor added together, it is called a synergistic effect, and implies that these factors interact in some way to create this larger-than-expected effect. While the underlying mechanism warrants further study, the review noted that COCs and obesity seems to increase a pro-inflammatory state in young women that can trigger adverse cardiovascular outcomes.
How does this inform what we already know about blood clots, obesity, and HBC?
While the relationship between cardiovascular disease and body mass has been well documented for some time, and the relationship between HBC and blood clots is also well known, the synergistic effect of obesity and estrogen-containing birth control helps us to understand the underlying cause of this important side effect, namely, how these conditions cause an increase in certain inflammatory markers [3][4][5]. This could be an excellent area for future research to better understand the effect birth control has on the body and how different conditions may affect one another, especially in women’s bodies.
Real caution is warranted when obese or overweight women consider taking HBC
This relationship also confirms that women with elevated BMI should exercise caution when considering whether to continue or start HBC. Blood clots are a relatively common occurrence, with 1-2 per every 1,000 people in the US experiencing a blood clot each year. 60% of these are DVTs alone and the other 40% are diagnosed as pulmonary embolisms (blood clot in the lungs) with or without DVTs [1]. A 2018 literature review in The Linacre Quarterly suggested that even among healthy young women in the U.S., 300-400 would be expected to die of blood clots related to their HBC use every year [3].
Women with elevated BMI (BMI of 25-29 is considered overweight and greater than 30 is considered obese), who are independently at risk for cardiovascular problems, should be made aware that—although many doctors consider the risk of developing DVT as a result of using HBC to be relatively small and counsel their patients accordingly—the risk for COC users coupled with obesity is much greater, 12 to 24 times higher than in women without these risk factors. Knowing the risk of potential side effects relative to your unique circumstances is an essential factor in giving informed consent to being prescribed and taking medication.
FAM: Reproductive care with no side effects
The recommendations given by the review authors were for doctors to prescribe progestin-only contraceptives instead of products containing estrogen in order to circumvent the increased risk of blood clots in obese or overweight patients. However, progestin-only contraceptives like Opill or Depo Provera (more on Depo Provera’s long-term effects on fertility here) carry their own risks and side effects that also need to be carefully considered before starting or continuing use.
Instead of simply trying to identify which birth control will cause the least number of troubling side effects, these side effects can be avoided altogether with the use of a fertility awareness method, which still allows women to avoid or space pregnancies as desired. Especially with the serious threat to overall health that DVTs pose, women with higher BMIs deserve to be well educated on their options in order to best protect their cardiovascular health.
Why worry if the risk is still low overall?
There are plenty of “probably won’t happen” risks that I avoid in my everyday life because the steps needed to avoid the risk are relatively easy, and the potential risk is sufficiently concerning. I use a seatbelt whenever I drive, not because I expect to get in a car crash, but because it’s a simple step that can protect me from serious harm in the unlikely event of an accident. I avoid giving honey to my infant, not because I expect she would contract infant botulism, but because it’s super easy to avoid and can prevent serious illness. I also use fertility awareness methods to track my cycles and space pregnancies, not because I expect that I would develop a blood clot while on birth control, but because my FAM is easy to use, helps me monitor my health, supports good communication with my spouse, and helps me entirely avoid the side effects and risks of using hormonal birth control.
References:
[1] Rosano, Giuseppe et al. “Obesity and contraceptive use: impact on cardiovascular risk.” ESC Heart Failure, vol. 9, no. 6 (2022): pp. 3761-67. https://doi.org/10.1002/ehf2.14104 [2] Severinsen, Marianne Tang et al. “Anthropometry, body fat, and venous thromboembolism: a Danish follow-up study.” Circulation vol. 120,19 (2009): pp. 1850-7. doi:10.1161/CIRCULATIONAHA.109.863241 [3] Csige, Imre et al. “The Impact of Obesity on the Cardiovascular System.” Journal of diabetes research (2018): 3407306. doi:10.1155/2018/3407306 [4] Powell-Wiley, Tiffany M et al. “Obesity and Cardiovascular Disease: A Scientific Statement From the American Heart Association.” Circulation vol. 143, no. ,21 (2021): e984-e1010. doi:10.1161/CIR.0000000000000973 [5] Keenan L, Kerr T, Duane M, Van Gundy K. “Systematic Review of Hormonal Contraception and Risk of Venous Thrombosis.” Linacre Q, vol. 85, no. 4 (2018): pp. 470-77. doi: 10.1177/0024363918816683. Epub 2019 Jan 3. PMID: 32431379; PMCID: PMC6322116.Additional Reading:
Knee surgery, blood clots, and birth control: The risks young female athletes need to know about
How a blood clot during pregnancy lead me to fertility awareness
