“Doctor explains why knee injuries are 3-times more common in teenage girls,” ran a 2022 headline from Fox’s affiliate station in Atlanta, GA. “Knee surgery rates soaring among teen girls” Reuters reported similarly in 2017. Of course, these headlines come as no surprise to anyone who has observed (or played) female middle school, high school, or college athletics in the past few decades, where knee injuries always seem to sideline more than a few talented young women. Many times, these injuries require intense surgical correction and extended physical rehabilitation, which can be devastating to the young women pinning their hopes and dreams on athletic success. Even more concerning is the elevated risk for blood clots after knee surgery, which can be deadly.
Knee arthroscopy, a minimally invasive procedure used to diagnose and treat joint problems, is the most common orthopedic surgery performed worldwide and is generally considered to be safe. However, after seeing several young, otherwise healthy women develop serious blood clots following various knee surgery procedures, a team of researchers recently investigated the connection between hormonal birth control use and increased risk for blood clots after the two most common knee surgeries amongst female athletes: knee arthroscopy and anterior cruciate ligament (ACL) reconstruction. They published their findings in the journal Arthroscopy in 2021, and what they found should concern any young female athlete on hormonal contraception.
The well-known connection between birth control and blood clots
The study’s research question relies on the well-known fact that contraceptive drugs increase the risk of blood clots. Dating as far back as the 1970s, studies have repeatedly found that birth control pills cause a hypercoagulable state (i.e., they make blood more prone to clotting) and have a direct effect on the blood vessels .
The most recent data suggests that out of every 10,000 women who are neither pregnant nor using birth control pills, between 1 and 5 will experience a blood clot every year. Of those using birth control pills, between 3 and 9 in every 10,000 will experience a blood clot. In absolute terms, that may be a small number, but it is roughly double the rate of non-users.
The reasons for this increased risk are well-known: many birth control pills contain estrogen, and higher levels of estrogen increase the blood’s ability to clot. Similarly, the FDA reports that progestin hormones present in some newer-generation birth control pills such as Yaz, Yasmin, and Desogen may also increase the blood’s ability to clot . Furthermore, oral contraceptive use in female athletes has been shown to markedly elevate levels of oxidative stress, which may also increase cardiovascular risks (such as the risk of thromboembolism) .
Female athletes, surgery, and blood clots: What the study found
The authors of the 2021 Arthroscopy study merely took the well-documented connection between birth control and blood clots a step further. Many of the researchers who took part in the study are orthopedic surgeons who were concerned to witness serious complications following these “low-risk” knee procedures in young athletes. Realizing that oral birth control use was common among many of these patients, they decided to investigate. As co-author Dr. Harris Slone, an orthopedic surgeon in South Carolina, told MedPage Today, “We know that the estrogen and progesterone in combination oral contraception pills increase the risk of clots. And we know that clots are problematic following orthopedic surgery, especially surgery around the pelvis, hip, and knee. But there has been little research to date quantifying the risk of oral contraception plus orthopedic surgery.”
So, using a large healthcare database, the team identified all women aged 16 to 40 who had undergone knee arthroscopy or ACL reconstruction between 2010 and 2015 and tracked two serious types of blood clots occurring within 90 days of surgery: deep vein thrombosis (DVT), a blood clot in a major blood vessel, and pulmonary embolism (PE), a blood clot in a lung. They tracked post-surgery incidences of these serious types of clots in both 1) women who were using combined oral contraceptives, and 2) women who were not using combined oral contraceptives. They also accounted for other risk factors, including obesity and smoking.
The research team’s findings were definitive and concerning: They found that the risk for these serious blood clots more than doubled in those taking oral contraceptives, while obesity and smoking increased the risk even more.
For patients without the risk factors of obesity and oral contraception use, the overall risk of clots was 0.95%. The risk rose to 1.72% in those using oral contraception, and to 3.13% in those who were both obese and taking birth control. The risk of blot clots was 1.24% for smokers, while the risk for smokers taking birth control climbed to 4.04%.
The author’s concluding suggestions won’t solve the problem
Given these findings, the study authors suggest that those taking oral contraceptives should be counseled regarding their increased risk for blood clots. They also suggested that patients would benefit from stopping their birth control use one month prior to surgery, or that they should consider postoperative anticoagulants if their risk factors remained.
Though the authors successfully quantify the risks involved in undergoing orthopedic surgery while on oral birth control, their suggestions to offset that risk have issues of their own. First, ACL reconstruction is typically scheduled between three and six weeks after the injury occurs, meaning that many women would not have sufficient time to rid their bodies of the artificial hormones’ effects. Second, additional evidence is needed to prove that stopping birth control use one month prior to surgery would lower the risk of clotting.
Finally, the postoperative anticoagulants the authors recommend in order to prevent blood clots also come with significant risks. Due to their potential for harm, oral anticoagulants have been classified as high alert medications by the Institute of Safe Medication Practices (ISMP) . A 2014 study suggested that two of the most commonly used blood thinners, warfarin (Coumadin) and low-molecular weight heparin (LMWH), known as Lovenox, are associated with an increased risk of post-surgery bleeding or infection .
Can getting off the Pill and learning fertility awareness help prevent knee injuries in the first place?
The young athletes who most commonly undergo these surgeries deserve to understand the increased risks they incur by taking birth control. In fact, this Arthroscopy study directly contradicts the consensus reached in a 2022 study published in JAMA Network Open, which found “no adverse outcomes” associated with the use of hormonal contraceptives.
Unfortunately, recommendations by many prominent health organizations continue to downplay the significant blood clot risks that accompany hormonal birth control use. As the title of an article on the Cleveland Clinic’s website puts it, “Yes, your birth control could make you more likely to have a blood clot. For most young women, it’s not necessarily a reason to stop taking the pill.” The National Women’s Health Network likewise characterizes the increased risk as being only “slightly higher.”
But the truth is, young women have a lot to benefit from getting off the Pill for good, even beyond lowering their risks for blood clots. In fact, recent studies suggest that Fertility Awareness Methods (FAMs) can help prevent sports injuries from occurring at all.
For example, in a 2021 study published in Frontiers in Sports and Active Living, researchers found that “muscle and tendon injury rates were 88% greater in the late follicular phase compared to the follicular phase, with muscle rupture/tear/strain/cramps and tendon injuries/ruptures occurring over twice as often during the late follicular phase compared to other phases .” Since teen girls and women who track their cycles learn to identify the four distinct phases (menstrual, follicular, ovulatory, and luteal), they could logically use this knowledge to inform their training plans and sharply reduce their chances of sustaining an injury (and, by extension, their risks of ever needing corrective surgery).
How FAMs can help female athletes train smarter
Reduced risk for injury is only one advantage of using fertility awareness as a training tool. The U.S. women’s national soccer team (USWNT) trains according to their cycles, and former coach Dawn Scott told Good Morning America that it’s “one of many strategies that we deployed that helped us win [the World Cup]” in 2019.
Scott, who coached the USWNT for a decade, observed that many players had consistent symptoms every month that impacted their performance and energy levels. She consulted with the founders of the period-tracking app Fitr Woman and had players track their menstrual cycles and related symptoms. Using that information, Scott built a profile for each player to individualize their sleep, hydration, nutrition, and recovery strategies.
In doing so, the team harnessed the power of “cycle syncing,” which Hanna Cox defined in an article for Natural Womanhood as “the practice of eating, exercising and aligning your schedule with the different phases of your natural menstrual cycle.” Women who track their cycles know not only when to expect their periods, but also how to track hormonal fluctuations and connect them to their symptoms. In this way, fertility awareness methods can allow athletes to be in tune with their bodies, to train smarter, and to better avoid devastating injuries and the subsequent risks of surgery.
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 U.S. Food & Drug Administration (FDA), FDA Drug Safety Communication: Updated information about the risk of blood clots in women taking birth control pills containing drospirenone, Rockville (MD): FDA, 2013.
 Cauci, S., Buligan, C., Marangone, M. et al. Oxidative Stress in Female Athletes Using Combined Oral Contraceptives. Sports Med – Open 2, 40 (2016). https://doi.org/10.1186/s40798-016-0064-x
 Amaraneni A, Chippa V, Rettew AC. Anticoagulation Safety. [Updated 2022 Jan 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519025/
 Wang Z, et al. “Surgical site infections and other postoperative complications following prophylactic anticoagulation in total joint arthroplasty.” PLoS One, vol. 9, no. 4, 2014. doi: 10.1371/journal.pone.0091755. PMID: 24717837; PMCID: PMC3981661.
 Martin D, et al. “Injury Incidence Across the Menstrual Cycle in International Footballers.” Frontiers in Sports and Active Living, vol 3, 616999, 2021. Doi: 10.3389/fspor.2021.616999.
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